Error after domain change

Error name:
There was an error trying to send your message. Please try again later.

Reason:
Doman change from:
sub.domain.com
to
doman.com

Website is working correctly however none of our contact form doesn’t.
We investigate into reCHAPTA plugging and all looks fine.

All fields like
[my-email]
[your-email]
[text-field]
so on… are ok.

Whole form was working before swooping domain. Where I can start looking for the reason of this error?

Regards

The page I need help with: [log in to see the link]