diff --git a/.github/workflows/php-cs.yml b/.github/workflows/php-cs.yml
new file mode 100644
index 0000000..7c09cdd
--- /dev/null
+++ b/.github/workflows/php-cs.yml
@@ -0,0 +1,36 @@
+on:
+    push:
+        paths:
+            - '**.php'
+    pull_request:
+        paths:
+            - '**.php'
+
+name: phpcs
+
+jobs:
+    phpcs:
+        runs-on: ubuntu-latest
+        steps:
+            - uses: actions/checkout@v2
+              with:
+                ref: ${{ github.head_ref }}
+
+            - name: check php version
+              run: php -v
+
+            - name: download phpcs
+              run: wget -O phpcs.phar https://cs.symfony.com/download/php-cs-fixer-v3.phar
+
+            - name: make phpcs executable
+              run: chmod +x phpcs.phar
+
+            - name: apply coding style
+              run: php phpcs.phar fix
+
+            - name: remove phpcs
+              run: rm -f phpcs.phar
+
+            - uses: stefanzweifel/git-auto-commit-action@v4
+              with:
+                  commit_message: 'phpcs: apply coding style'
diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..0ac0100
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,5 @@
+/vendor
+/example.php
+/composer.lock
+/notify.php
+/notify.log
\ No newline at end of file
diff --git a/.php-cs-fixer.dist.php b/.php-cs-fixer.dist.php
new file mode 100644
index 0000000..4a2f428
--- /dev/null
+++ b/.php-cs-fixer.dist.php
@@ -0,0 +1,17 @@
+<?php
+
+use PhpCsFixer\Finder;
+use PhpCsFixer\Config;
+
+$directories = ['vendor'];
+$finder = Finder::create()
+    ->in(__DIR__)
+    ->exclude($directories);
+
+return (new Config())
+    ->setRules([
+        '@PSR2' => true,
+    ])
+    ->setRiskyAllowed(true)
+    ->setUsingCache(false)
+    ->setFinder($finder);
diff --git a/composer.json b/composer.json
new file mode 100644
index 0000000..929928c
--- /dev/null
+++ b/composer.json
@@ -0,0 +1,24 @@
+{
+    "name": "zerosdev/tripay-sdk-php",
+    "description": "Unofficial TriPay.co.id Integration Kit for PHP",
+    "type": "library",
+    "require": {
+        "php": ">=7.2.0",
+        "ext-curl": "*",
+        "ext-json": "*",
+        "guzzlehttp/guzzle": "^6.5|^7.0"
+    },
+    "license": "MIT",
+    "authors": [
+        {
+            "name": "ZerosDev",
+            "email": "ronywisnuwardana@gmail.com"
+        }
+    ],
+    "minimum-stability": "stable",
+    "autoload": {
+        "psr-4": {
+            "ZerosDev\\TriPay\\": "src/"
+        }
+    }
+}
diff --git a/src/Callback.php b/src/Callback.php
new file mode 100644
index 0000000..365a44d
--- /dev/null
+++ b/src/Callback.php
@@ -0,0 +1,109 @@
+<?php
+
+namespace ZerosDev\TriPay;
+
+use Exception;
+use UnexpectedValueException;
+use ZerosDev\TriPay\Exception\SignatureException;
+
+class Callback
+{
+    /**
+     * Client instance
+     *
+     * @var Client
+     */
+    protected Client $client;
+
+    /**
+     * Callback json data
+     *
+     * @var string
+     */
+    protected string $json = "";
+
+    /**
+     * Parsed callback json data
+     *
+     * @var object|null
+     */
+    protected ?object $parsedJson;
+
+    /**
+     * Callback instance
+     *
+     * @param Client $client
+     * @param bool $verifyOnLoad
+     */
+    public function __construct(Client $client, bool $verifyOnLoad = true)
+    {
+        if (!function_exists('file_get_contents')) {
+            throw new Exception('`file_get_contents` function is disabled on your system. Please contact your hosting provider');
+        }
+
+        $this->client = $client;
+        $this->json = (string) file_get_contents("php://input");
+        $this->parsedJson = json_decode($this->json);
+
+        if ($verifyOnLoad) {
+            $this->validate();
+        }
+    }
+
+    /**
+     * Get local signature
+     *
+     * @return string
+     */
+    public function localSignature(): string
+    {
+        return (string) hash_hmac('sha256', $this->json, $this->client->privateKey);
+    }
+
+    /**
+     * Get incoming signature
+     *
+     * @return string|null
+     */
+    public function incomingSignature(): ?string
+    {
+        return (string) (isset($_SERVER['HTTP_X_CALLBACK_SIGNATURE']) ? $_SERVER['HTTP_X_CALLBACK_SIGNATURE'] : "");
+    }
+
+    /**
+     * Validate incoming signature
+     *
+     * @return boolean
+     * @throws SignatureException
+     * @throws UnexpectedValueException
+     */
+    public function validate(): bool
+    {
+        $validSignature = hash_equals(
+            $this->localSignature(),
+            $this->incomingSignature()
+        );
+
+        if (!$validSignature) {
+            throw new SignatureException('Incoming signature does not match local signature');
+        }
+
+        $validData = !is_null($this->data());
+
+        if (!$validData) {
+            throw new UnexpectedValueException('Callback data is invalid');
+        }
+
+        return true;
+    }
+
+    /**
+     * Parse JSON data
+     *
+     * @return object|null
+     */
+    public function data(): ?object
+    {
+        return $this->parsedJson;
+    }
+}
diff --git a/src/Client.php b/src/Client.php
new file mode 100644
index 0000000..45e08f7
--- /dev/null
+++ b/src/Client.php
@@ -0,0 +1,192 @@
+<?php
+
+namespace ZerosDev\TriPay;
+
+use GuzzleHttp\Client as HttpClient;
+use GuzzleHttp\Psr7\Response;
+use GuzzleHttp\TransferStats;
+use InvalidArgumentException;
+use ZerosDev\TriPay\Support\Constant;
+
+class Client
+{
+    /**
+     * Merchant Code
+     *
+     * @var string|null
+     */
+    public ?string $merchantCode;
+
+    /**
+     * API Key
+     *
+     * @var string|null
+     */
+    public ?string $apiKey;
+
+    /**
+     * Private Key
+     *
+     * @var string|null
+     */
+    public ?string $privateKey;
+
+    /**
+     * API mode
+     *
+     * @var string|null
+     */
+    public ?string $mode;
+
+    /**
+     * Request payloads
+     *
+     * @var array
+     */
+    public array $payloads = [];
+
+    /**
+     * Debugs payload
+     *
+     * @var array
+     */
+    public array $debugs = [
+        'request' => null,
+        'response' => null,
+    ];
+
+    /**
+     * Required configuration key
+     *
+     * @var array
+     */
+    private array $requiredConfigKeys = [
+        'merchant_code',
+        'api_key',
+        'private_key',
+        'mode'
+    ];
+
+    /**
+     * Reserved guzzle options that can't be overrided
+     *
+     * @var array
+     */
+    private array $reservedGuzzleOptions = [
+        'base_uri',
+        'on_stats',
+    ];
+
+    /**
+     * HTTP Client instance
+     *
+     * @var GuzzleHttp\Client as HttpClient
+     */
+    private HttpClient $client;
+
+    /**
+     * Client instance
+     *
+     * You can use array config with the following keys
+     * [
+     *      'merchant_id' => '',
+     *      'api_key' => '',
+     *      'private_key' => '',
+     *      'mode => '',
+     *      'guzzle_options' => []
+     * ]
+     *
+     * or use the positional arguments in the following sequence
+     * $merchantId, $apiKey, $privateKey, $mode, $guzzleOptions
+     *
+     * @param array|string ...$args
+     * @throws InvalidArgumentException
+     */
+    public function __construct(...$args)
+    {
+        if (is_array($args[0])) {
+            foreach ($this->requiredConfigKeys as $configKey) {
+                if (!isset($args[0][$configKey])) {
+                    throw new InvalidArgumentException("`{$configKey}` must be in the configuration value");
+                }
+            }
+        } else {
+            foreach ($this->requiredConfigKeys as $key => $configKey) {
+                if (!isset($args[$key])) {
+                    throw new InvalidArgumentException("`{$configKey}` must be in the configuration value");
+                }
+            }
+        }
+
+        $this->merchantCode = (string) is_array($args[0]) ? $args[0]['merchant_code'] : $args[0];
+        $this->apiKey = (string) is_array($args[0]) ? $args[0]['api_key'] : $args[1];
+        $this->privateKey = (string) is_array($args[0]) ? $args[0]['private_key'] : $args[1];
+        $this->mode = (string) is_array($args[0]) ? $args[0]['mode'] : $args[2];
+
+        $baseUri = ($this->mode == Constant::MODE_DEVELOPMENT)
+            ? Constant::URL_DEVELOPMENT
+            : Constant::URL_PRODUCTION;
+
+        $options = [
+            'base_uri' => $baseUri,
+            'http_errors' => false,
+            'connect_timeout' => 10,
+            'timeout' => 50,
+            'on_stats' => function (TransferStats $stats) {
+                $hasResponse = $stats->hasResponse();
+                $this->debugs = array_merge($this->debugs, [
+                    'request' => [
+                        'url' => (string) $stats->getEffectiveUri(),
+                        'method' => $stats->getRequest()->getMethod(),
+                        'headers' => (array) $stats->getRequest()->getHeaders(),
+                        'body' => (string) $stats->getRequest()->getBody(),
+                    ],
+                    'response' => [
+                        'status' => (int) ($hasResponse ? $stats->getResponse()->getStatusCode() : 0),
+                        'headers' => (array) ($hasResponse ? $stats->getResponse()->getHeaders() : []),
+                        'body' => (string) ($hasResponse ? $stats->getResponse()->getBody() : ""),
+                    ],
+                ]);
+            },
+            'headers' => [
+                'Authorization' => 'Bearer ' . $this->apiKey,
+                'User-Agent' => 'zerosdev/tripay-sdk-php',
+            ]
+        ];
+
+        $guzzleOptions = (array) is_array($args[0]) ? ($args[0]['guzzle_options'] ?? []) : ($args[3] ?? []);
+
+        foreach ($this->reservedGuzzleOptions as $reserved) {
+            unset($guzzleOptions[$reserved]);
+        }
+
+        $options = array_merge($options, $guzzleOptions);
+
+        $this->client = $this->createHttpClient($options);
+    }
+
+    private function createHttpClient(array $options): HttpClient
+    {
+        return new HttpClient($options);
+    }
+
+    public function get($endpoint, array $headers = []): Response
+    {
+        return $this->client->get($endpoint, [
+            'headers' => $headers,
+        ]);
+    }
+
+    public function post($endpoint, array $payloads, array $headers = []): Response
+    {
+        return $this->client->post($endpoint, [
+            'json' => $payloads,
+            'headers' => $headers,
+        ]);
+    }
+
+    public function debugs(): object
+    {
+        return (object) $this->debugs;
+    }
+}
diff --git a/src/Exception/SignatureException.php b/src/Exception/SignatureException.php
new file mode 100644
index 0000000..fb9822d
--- /dev/null
+++ b/src/Exception/SignatureException.php
@@ -0,0 +1,10 @@
+<?php
+
+namespace ZerosDev\TriPay\Exception;
+
+use Exception;
+
+class SignatureException extends Exception
+{
+    //
+}
diff --git a/src/Merchant.php b/src/Merchant.php
new file mode 100644
index 0000000..431d1da
--- /dev/null
+++ b/src/Merchant.php
@@ -0,0 +1,67 @@
+<?php
+
+namespace ZerosDev\TriPay;
+
+use GuzzleHttp\Psr7\Response;
+use ZerosDev\TriPay\Support\Helper;
+
+class Merchant
+{
+    /**
+     * Client instance
+     *
+     * @var Client
+     */
+    protected Client $client;
+
+    /**
+     * Merchant instance
+     *
+     * @param Client $client
+     */
+    public function __construct(Client $client)
+    {
+        $this->client = $client;
+    }
+
+    /**
+     * Get enabled payment channels
+     *
+     * @return Response
+     */
+    public function paymentChannels(): Response
+    {
+        return $this->client->get('merchant/payment-channel');
+    }
+
+    /**
+     * Get fee calculation
+     *
+     * @param mixed $amount
+     * @param string|null $channelCode
+     * @return Response
+     */
+    public function feeCalculator($amount, ?string $channelCode = null): Response
+    {
+        $payloads = [
+            'amount' => Helper::formatAmount($amount),
+        ];
+
+        if (!empty($channelCode)) {
+            $payloads['code'] = $channelCode;
+        }
+
+        return $this->client->get('merchant/fee-calculator?' . http_build_query($payloads));
+    }
+
+    /**
+     * Get merchant transactions
+     *
+     * @param array $payloads
+     * @return Response
+     */
+    public function transactions(array $payloads = []): Response
+    {
+        return $this->client->get('merchant/transactions?' . http_build_query($payloads));
+    }
+}
diff --git a/src/OpenPayment.php b/src/OpenPayment.php
new file mode 100644
index 0000000..82c433e
--- /dev/null
+++ b/src/OpenPayment.php
@@ -0,0 +1,68 @@
+<?php
+
+namespace ZerosDev\TriPay;
+
+use GuzzleHttp\Psr7\Response;
+use ZerosDev\TriPay\Support\Helper;
+
+class OpenPayment
+{
+    /**
+     * Client instance
+     *
+     * @var Client
+     */
+    protected Client $client;
+
+    /**
+     * OpenPayment instance
+     *
+     * @param Client $client
+     */
+    public function __construct(Client $client)
+    {
+        $this->client = $client;
+    }
+
+    /**
+     * Create open payment
+     *
+     * @param array $payloads
+     * @return Response
+     * @throws InvalidArgumentException
+     */
+    public function create(array $payloads): Response
+    {
+        unset($payloads['signature']);
+
+        Helper::checkRequiredPayloads([
+            'method'
+        ], $payloads);
+
+        $payloads['signature'] = Helper::makeOpenPaymentSignature($this->client, $payloads);
+
+        return $this->client->post('open-payment/create', $payloads);
+    }
+
+    /**
+     * Get open payment detail
+     *
+     * @param string $uuid
+     * @return Response
+     */
+    public function detail(string $uuid): Response
+    {
+        return $this->client->get('open-payment/' . $uuid . '/detail');
+    }
+
+    /**
+     * Get open payment transactions
+     *
+     * @param string $uuid
+     * @return Response
+     */
+    public function transactions(string $uuid): Response
+    {
+        return $this->client->get('open-payment/' . $uuid . '/transactions');
+    }
+}
diff --git a/src/Payment.php b/src/Payment.php
new file mode 100644
index 0000000..3a40424
--- /dev/null
+++ b/src/Payment.php
@@ -0,0 +1,56 @@
+<?php
+
+namespace ZerosDev\TriPay;
+
+use GuzzleHttp\Psr7\Response;
+use ZerosDev\TriPay\Support\Helper;
+
+class Payment
+{
+    /**
+     * Client instance
+     *
+     * @var Client
+     */
+    protected Client $client;
+
+    /**
+     * Payment instance
+     *
+     * @param Client $client
+     */
+    public function __construct(Client $client)
+    {
+        $this->client = $client;
+    }
+
+    /**
+     * Get payment channel instruction
+     *
+     * @param string $channelCode
+     * @param string|null $payCode
+     * @param mixed $amount
+     * @param integer|null $allowHtml
+     * @return Response
+     */
+    public function instruction(string $channelCode, ?string $payCode = null, $amount = null, ?int $allowHtml = null): Response
+    {
+        $payloads = [
+            'code' => $channelCode
+        ];
+
+        if (!is_null($payCode)) {
+            $payloads['pay_code'] = $payCode;
+        }
+
+        if (!is_null($amount)) {
+            $payloads['amount'] = $amount;
+        }
+
+        if (!is_null($allowHtml)) {
+            $payloads['allow_html'] = $allowHtml;
+        }
+
+        return $this->client->get('payment/instruction?' . http_build_query($payloads));
+    }
+}
diff --git a/src/Support/Constant.php b/src/Support/Constant.php
new file mode 100644
index 0000000..7924f5c
--- /dev/null
+++ b/src/Support/Constant.php
@@ -0,0 +1,12 @@
+<?php
+
+namespace ZerosDev\TriPay\Support;
+
+class Constant
+{
+    public const URL_DEVELOPMENT = 'https://tripay.co.id/api-sandbox/';
+    public const URL_PRODUCTION = 'https://tripay.co.id/api/';
+
+    public const MODE_DEVELOPMENT = 'development';
+    public const MODE_PRODUCTION = 'production';
+}
diff --git a/src/Support/Helper.php b/src/Support/Helper.php
new file mode 100644
index 0000000..b96214c
--- /dev/null
+++ b/src/Support/Helper.php
@@ -0,0 +1,73 @@
+<?php
+
+namespace ZerosDev\TriPay\Support;
+
+use Exception;
+use InvalidArgumentException;
+use ZerosDev\TriPay\Client;
+
+class Helper
+{
+    /**
+     * Create signature
+     *
+     * @param ZerosDev\TriPay\Client $client
+     * @param array $payloads
+     * @return string
+     */
+    public static function makeSignature(Client $client, array $payloads): string
+    {
+        $merchantRef = isset($payloads['merchant_ref']) ? $payloads['merchant_ref'] : null;
+        $amount = self::formatAmount($payloads['amount']);
+
+        $payloads['amount'] = self::formatAmount($payloads['amount']);
+        return hash_hmac('sha256', $client->merchantCode . $merchantRef . $amount, $client->privateKey);
+    }
+
+    /**
+     * Create open payment signature
+     *
+     * @param ZerosDev\TriPay\Client $client
+     * @param array $payloads
+     * @return string
+     */
+    public static function makeOpenPaymentSignature(Client $client, array $payloads): string
+    {
+        $method = isset($payloads['method']) ? $payloads['method'] : null;
+        $merchantRef = isset($payloads['merchant_ref']) ? $payloads['merchant_ref'] : null;
+
+        return hash_hmac('sha256', $client->merchantCode . $method . $merchantRef, $client->privateKey);
+    }
+
+    /**
+     * Format amount to integer
+     *
+     * @param mixed $amount
+     * @return int
+     */
+    public static function formatAmount($amount): int
+    {
+        if (!is_numeric($amount)) {
+            throw new Exception('Amount must be numeric value');
+        }
+
+        return (int) number_format($amount, 0, '', '');
+    }
+
+    /**
+     * Check required key in payloads
+     *
+     * @param array $requireds
+     * @param array $payloads
+     * @return void
+     * @throws InvalidArgumentException
+     */
+    public static function checkRequiredPayloads(array $requireds, array $payloads): void
+    {
+        foreach ($requireds as $req) {
+            if (!isset($payloads[$req]) || empty($payloads[$req])) {
+                throw new InvalidArgumentException("`{$req}` must be filled in payloads");
+            }
+        }
+    }
+}
diff --git a/src/Transaction.php b/src/Transaction.php
new file mode 100644
index 0000000..3879029
--- /dev/null
+++ b/src/Transaction.php
@@ -0,0 +1,98 @@
+<?php
+
+namespace ZerosDev\TriPay;
+
+use GuzzleHttp\Psr7\Response;
+use ZerosDev\TriPay\Support\Helper;
+
+class Transaction
+{
+    /**
+     * Client instance
+     *
+     * @var Client
+     */
+    protected Client $client;
+
+    /**
+     * Order items
+     *
+     * @var array
+     */
+    protected array $order_items = [];
+
+    /**
+     * Transaction instance
+     *
+     * @param Client $client
+     */
+    public function __construct(Client $client)
+    {
+        $this->client = $client;
+    }
+
+    /**
+     * Add order items to payloads
+     *
+     * @param string $name
+     * @param integer $price
+     * @param integer $quantity
+     * @param string|null $sku
+     * @param string|null $product_url
+     * @param string|null $image_url
+     * @return self
+     */
+    public function addOrderItem(string $name, int $price, int $quantity, ?string $sku = null, ?string $product_url = null, ?string $image_url = null): self
+    {
+        $this->order_items[] = [
+            'sku' => $sku,
+            'name' => $name,
+            'price' => $price,
+            'quantity' => $quantity,
+            'product_url' => $product_url,
+            'image_url' => $image_url,
+        ];
+
+        return $this;
+    }
+
+    /**
+     * Create transaction
+     *
+     * @param array $payloads
+     * @return Response
+     * @throws InvalidArgumentException
+     */
+    public function create(array $payloads): Response
+    {
+        unset($payloads['signature']);
+
+        $payloads['order_items'] = isset($payloads['order_items'])
+            ? array_merge($payloads['order_items'], $this->order_items)
+            : $this->order_items;
+
+        $payloads['amount'] = 0;
+        foreach ($this->order_items as $orderItem) {
+            $payloads['amount'] += $orderItem['price'] * $orderItem['quantity'];
+        }
+
+        Helper::checkRequiredPayloads([
+            'method', 'customer_name', 'customer_email', 'order_items'
+        ], $payloads);
+
+        $payloads['signature'] = Helper::makeSignature($this->client, $payloads);
+
+        return $this->client->post('transaction/create', $payloads);
+    }
+
+    /**
+     * Get transaction detail
+     *
+     * @param string $reference
+     * @return Response
+     */
+    public function detail(string $reference): Response
+    {
+        return $this->client->get('transaction/detail?reference=' . $reference);
+    }
+}