Contact Form failure


#1

This is our website: http://www.macgregor.edu.hk/ielts/?lang=en

Open the console, everything is fine. However, when I like to submit a ninja form at the bottom (“Inquire Now”) it shows the below error. I checked some article, eg https://wordpress.org/support/topic/403-on-admin-ajax-php/
Asked CW but said everything fine at server side.

Any idea? Thanks!

#PS The subscription form at the bottom works fine. It is a Contact Form 7

THE ERROR in Chrome Console:

Failed to load resource: the server responded with a status of 403 (Forbidden) /wp-admin/admin-ajax.php

And following this:
ERRORS: Forbidden
front-end.js:2 Object
front-end.js:2 Notice: Error trying to reset grecaptcha.
front-end.js:2 Parse Error
front-end.js:2 Notice: Error trying to reset grecaptcha.
front-end.js:1 Uncaught TypeError: Cannot read property ‘fields’ of undefined
at n.submitErrors (front-end.js:1)
at _ (backbone.min.js:1)
at m (backbone.min.js:1)
at f (backbone.min.js:1)
at u.Channel.u.trigger (backbone.min.js:1)
at Object.error (front-end.js:2)
at i (jquery.js:2)
at Object.fireWith [as rejectWith] (jquery.js:2)
at y (jquery.js:4)
at XMLHttpRequest.c (jquery.js:4)