To add a custom end point to the wp-rest api with the string param at the end. You can change the S+ with d+ for the integer param register_rest_route( ‘wp/v2’, ‘/data/(?P\S+)’, array( ‘methods’ => ‘GET’, ‘callback’ => ‘get_data’ ) ); function get_data($request){ $value = $request[‘data’]; //your code goes here } Ex: http://example.com/wp-json/wp/v2/data/test

Have you ever used give plugin for donation integration? Would you like to integrate any other payment gateway with the give plugin? Here is the simple code for the bluepay integration with give plugin. You can change the API’s for the other gateway if needed. Please go through the link here