Example implementation of a Wordpress function to process a POST request

custom-api-route-3.php

function process_data_submission(WP_REST_Request $request) {
    $data = json_decode($request->get_body(), true);

    // Perform your data processing here

    $response = new WP_REST_Response(array('status' => 'success', 'message' => 'Data processed successfully'));
    $response->set_status(200);
    return $response;
}