diff --git a/CHANGELOG.md b/CHANGELOG.md
index efbf652..93d7820 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,10 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [3.5.9] - 2026-05-08
+### Added
+- Refactor `checkoutSession` to extend `PaymentRequest` to enable support for all standard payment parameters.
+
 ## [3.5.8] - 2026-02-23
 ### Added
 - Add support for `checkoutSession` API method.
diff --git a/src/AbstractApi.php b/src/AbstractApi.php
index e415c70..3a3a239 100644
--- a/src/AbstractApi.php
+++ b/src/AbstractApi.php
@@ -55,7 +55,7 @@ abstract class AbstractApi
     /**
      * PHP API version
      */
-    const PHP_API_VERSION = '3.5.8';
+    const PHP_API_VERSION = '3.5.9';
 
     /**
      * Event dispatcher
diff --git a/src/Api/Payments/CheckoutSession.php b/src/Api/Payments/CheckoutSession.php
index 36dbc7b..d466ab9 100644
--- a/src/Api/Payments/CheckoutSession.php
+++ b/src/Api/Payments/CheckoutSession.php
@@ -23,19 +23,14 @@
 
 namespace Altapay\Api\Payments;
 
-use Altapay\AbstractApi;
-use Altapay\Exceptions\ClientException;
-use Altapay\Exceptions\ResponseHeaderException;
-use Altapay\Exceptions\ResponseMessageException;
-use Altapay\Serializer\ResponseSerializer;
+use Altapay\Api\Ecommerce\PaymentRequest;
 use Altapay\Response\CheckoutSessionResponse;
-use GuzzleHttp\Exception\ClientException as GuzzleHttpClientException;
-use GuzzleHttp\Exception\GuzzleException;
+use Altapay\Serializer\ResponseSerializer;
 use GuzzleHttp\Psr7\Request;
 use Psr\Http\Message\ResponseInterface;
 use Symfony\Component\OptionsResolver\OptionsResolver;
 
-class CheckoutSession extends AbstractApi
+class CheckoutSession extends PaymentRequest
 {
     /**
      * Set the list of terminals available for the user
@@ -51,76 +46,6 @@ public function setTerminals(array $terminals)
         return $this;
     }
 
-    /**
-     * Set optional session identifier
-     *
-     * @param string $sessionId
-     *
-     * @return $this
-     */
-    public function setSessionId($sessionId)
-    {
-        $this->unresolvedOptions['session_id'] = $sessionId;
-
-        return $this;
-    }
-
-    /**
-     * Set shop order ID
-     *
-     * @param string $shopOrderId
-     *
-     * @return $this
-     */
-    public function setShopOrderId($shopOrderId)
-    {
-        $this->unresolvedOptions['shop_orderid'] = $shopOrderId;
-
-        return $this;
-    }
-
-    /**
-     * Set amount
-     *
-     * @param float $amount
-     *
-     * @return $this
-     */
-    public function setAmount($amount)
-    {
-        $this->unresolvedOptions['amount'] = $amount;
-
-        return $this;
-    }
-
-    /**
-     * Set currency
-     *
-     * @param string $currency
-     *
-     * @return $this
-     */
-    public function setCurrency($currency)
-    {
-        $this->unresolvedOptions['currency'] = $currency;
-
-        return $this;
-    }
-
-    /**
-     * Set config parameters
-     *
-     * @param array<string, mixed> $config
-     *
-     * @return $this
-     */
-    public function setConfig(array $config)
-    {
-        $this->unresolvedOptions['config'] = $config;
-
-        return $this;
-    }
-
     /**
      * Configure options
      *
@@ -130,14 +55,9 @@ public function setConfig(array $config)
      */
     protected function configureOptions(OptionsResolver $resolver)
     {
+        parent::configureOptions($resolver);
         $resolver->setRequired(['terminals']);
-        $resolver->setDefined(['session_id', 'shop_orderid', 'amount', 'currency', 'config']);
         $resolver->addAllowedTypes('terminals', 'array');
-        $resolver->addAllowedTypes('session_id', 'string');
-        $resolver->addAllowedTypes('shop_orderid', 'string');
-        $resolver->addAllowedTypes('amount', ['int', 'float']);
-        $resolver->addAllowedTypes('currency', 'string');
-        $resolver->addAllowedTypes('config', 'array');
     }
 
     /**
@@ -157,17 +77,6 @@ protected function handleResponse(Request $request, ResponseInterface $response)
         return ResponseSerializer::serialize(CheckoutSessionResponse::class, $xml->Body, $xml->Header);
     }
 
-    /**
-     * @return array<string, string>
-     */
-    protected function getBasicHeaders()
-    {
-        $headers = parent::getBasicHeaders();
-        $headers['Content-Type'] = 'application/x-www-form-urlencoded';
-
-        return $headers;
-    }
-
     /**
      * Url to api call
      *
@@ -179,53 +88,4 @@ protected function getUrl(array $options)
     {
         return 'checkoutSession';
     }
-
-    /**
-     * @return string
-     */
-    protected function getHttpMethod()
-    {
-        return 'POST';
-    }
-
-    /**
-     * Generate the response
-     *
-     * @throws \Exception
-     * @throws ClientException
-     * @throws GuzzleException
-     * @throws ResponseHeaderException
-     * @throws ResponseMessageException
-     */
-    protected function doResponse()
-    {
-        $this->doConfigureOptions();
-        $headers = $this->getBasicHeaders();
-        $request = new Request(
-            $this->getHttpMethod(),
-            $this->parseUrl(),
-            $headers,
-            $this->getPostOptions()
-        );
-        $this->request = $request;
-        
-        try {
-            $response = $this->getClient()->send($request);
-            $this->response = $response;
-            $output = $this->handleResponse($request, $response);
-            $this->validateResponse($output);
-
-            return $output;
-        } catch (GuzzleHttpClientException $e) {
-            throw new ClientException($e->getMessage(), $e->getRequest(), $e->getResponse(), $e);
-        }
-    }
-
-    /**
-     * @return string
-     */
-    protected function getPostOptions()
-    {
-        return http_build_query($this->options, '', '&');
-    }
 }
diff --git a/src/Response/CheckoutSessionResponse.php b/src/Response/CheckoutSessionResponse.php
index cc4544a..2b6e39b 100644
--- a/src/Response/CheckoutSessionResponse.php
+++ b/src/Response/CheckoutSessionResponse.php
@@ -25,7 +25,7 @@
 
 use Altapay\Response\Embeds\Session;
 
-class CheckoutSessionResponse extends AbstractResponse
+class CheckoutSessionResponse extends PaymentRequestResponse
 {
     /**
      * Children of the response