Issues with Booking Plugin

I’ve been having issues for a while on chichestertennisacademy.co.uk and I think it’s being caused by Cleantalk… After submitting a booking request (no login required) there is an ajax 403 error and the booking is rejected with a network error on screen.

This issues is not 100% repeatable and does not always happen.

Looking at the logs I see over 100 contact form completions logged but you can see codes such as 1001 in the messages and I think Cleantalk is interrupting the workflow.

I have just disabled the plugin to see if any more customers report this issue but I would be greatful if you could look at recent activity for Chichestertennisacademy.co.uk and see if you can help me.