Error message when adding to cart:

"An unknown response null: :text/html: :Forbidden was received while processing an ajax call. The action you requested could not be completed."

Site bmamps.com/store
ZC 1.5.4
php 5.3.29
mySQL 5.6.33
Plugins: I'm really not sure. It was so long ago that I set t up I really can't remember. Sorry!

All was working well, no changes were made, at least on my side although the hosting service may have changed something without telling me, now I get this error.

I read this thread https://www.zen-cart.com/showthread....N-was-received and so checked my ajax.php was present and original

There is nothing in the debug log.

I'd really appreciate some help. Thanks.