Thanks for the awesome work on this plugin! This plugin has worked well in several environments, however we recently migrated a website over to Google Cloud & were unable to submit forms. We ultimately discovered that this was failing due to this specific check the plugin makes: In src/ajax.php

// check IP
if ($appointment['ip'] != $_SERVER['REMOTE_ADDR']) {
    $this->send_err_json_result('{"err":true}');
}

Because our Google Cloud setup runs with load balancers & pods, the IP's that the plugin checks would never match. Hoping that this can be resolved in a future update. Thank you again for your work on this plugin!