feat(checkout): allow customizing checkout query params via filter

Introduce a namespaced filter to let developers add/modify query params sent to Freemius Checkout.
	•	Add fs_apply_filter( $fs->get_unique_affix(), 'checkout_query_params', ... )

Author: DanieleFreemius

includes/class-freemius.php

@@ -365,15 +365,6 @@ class Freemius extends Freemius_Abstract {
          */
         private $_is_bundle_license_auto_activation_enabled = false;
 
-        /**
-         * Developer-defined config overrides for checkout.
-         *
-         * @var array
-         */
-        protected $_checkout_config = [];
-
-        /**
-
         #region Uninstall Reasons IDs
 
         const REASON_NO_LONGER_NEEDED = 1;
@@ -5190,9 +5181,6 @@ private function parse_settings( &$plugin_info ) {
                 ) );
             }
 
-            // Extracts, validate and save checkout-specific settings.
-            $this->_checkout_config = $this->validate_checkout_config( $plugin_info );
-
             $plugin = ( $this->_plugin instanceof FS_Plugin ) ?
                 $this->_plugin :
                 new FS_Plugin();
@@ -5334,88 +5322,6 @@ private function parse_settings( &$plugin_info ) {
             );
         }
 
-        /**
-         * Validates and filters developer-provided checkout config.
-         *
-         * @param array $config
-         *
-         * @return array
-         */
-        protected function validate_checkout_config($config)
-        {
-            $schema = array(
-                // currency
-                'currency'                      => 'string',
-                'default_currency'              => 'string',
-                // cart
-                'always_show_renewals_amount'   => 'bool',
-                'annual_discount'               => 'bool',
-                'billing_cycle'                 => ['string', 'int'],
-                'bundle_discount'               => 'float',
-                'maximize_discounts'            => 'bool',
-                'multisite_discount'            => ['bool', 'string'], // string expected to be "auto"
-                'show_inline_currency_selector' => 'bool',
-                'show_monthly'                  => 'bool',
-                // appearance
-                'form_position'                 => 'string',
-                'is_bundle_collapsed'           => 'bool',
-                'layout'                        => 'string',
-                'refund_policy_position'        => 'string',
-                'show_refund_badge'             => 'bool',
-                'show_reviews'                  => 'bool',
-                'show_upsells'                  => 'bool',
-                'title'                         => 'string',
-            );
-
-            $result = array();
-
-            foreach ($schema as $key => $expected_type)
-            {
-                if (array_key_exists($key, $config))
-                {
-                    $value = $config[$key];
-                    $types = is_array($expected_type) ? $expected_type : [$expected_type];
-                    $valid = false;
-
-                    foreach ($types as $type)
-                    {
-                        switch ($type)
-                        {
-                            case 'bool':
-                                if (is_bool($value))
-                                    $valid = true;
-                                break;
-                            case 'string':
-                                if (is_string($value))
-                                    $valid = true;
-                                break;
-                            case 'int':
-                                if (is_int($value))
-                                    $valid = true;
-                                break;
-                            case 'float':
-                                if (is_float($value) || is_int($value))
-                                    $valid = true;
-                                break;
-                        }
-                    }
-
-                    if ($valid)
-                        $result[$key] = $value;
-                }
-            }
-
-            return $result;
-        }
-
-        /**
-         * @return array
-         */
-        public function get_checkout_config()
-        {
-            return $this->_checkout_config;
-        }
-
         /**
          * @param string[] $options
          * @param string   $key

includes/managers/class-fs-checkout-manager.php

@@ -153,12 +153,37 @@ public function get_query_params( Freemius $fs, $plugin_id, $plan_id, $licenses
 				( $fs->is_theme() && current_user_can( 'install_themes' ) )
 			);
 
-            // Add developer-defined checkout overrides directly to context.
-            foreach ( $fs->get_checkout_config() as $key => $value ) {
-                $context_params[ $key ] = $value;
-            }
-
-			return array_merge( $context_params, $_GET, array(
+            /**
+             * Allow developers to customize the checkout query params before final validation,
+             * so custom keys can be included and known keys can be overridden.
+             * We then validate the merged params and re-attach any unknown custom keys that
+             * validation intentionally ignores, preserving developer-provided extras while
+             * keeping core keys safe.
+             *
+             * Usage example (in a plugin/theme):
+             *
+             *     add_filter( 'fs_checkout_query_params_' . fs()->get_unique_affix(), function( $params ) {
+             *         // Add or modify query params passed to the Freemius Checkout.
+             *         $params['coupon'] = 'WELCOME10';
+             *         $params['utm_source'] = 'my-plugin';
+             *         return $params;
+             *     }, 10, 5 );
+             *
+             * @since 2.12.1.3
+             *
+             * @param array     $context_params The params prepared by the SDK before validation.
+             * @param Freemius  $fs            The Freemius instance of the calling module.
+             * @param int|mixed $plugin_id     The target plugin/add-on ID for the checkout context.
+             * @param int|mixed $plan_id       The selected plan ID (if any).
+             * @param int|mixed $licenses      The requested number of licenses (if provided).
+             */
+            $filtered_params = fs_apply_filter(
+                $fs->get_unique_affix(),
+                'checkout_query_params',
+                $context_params
+            );
+
+			return array_merge( $filtered_params, $_GET, array(
 				// Current plugin version.
 				'plugin_version' => $fs->get_plugin_version(),
 				'sdk_version'    => WP_FS__SDK_VERSION,