Cannot save settings

Hi we recently installed this plugin on a website running our usual setup.

The settings screen wont save.

No errors in console just wont save.

So far I have deleted the plugin and installed it from a manual zip file to check for problems.

But this makes no difference.

Please can you advise?

There is nothing different about this site vs our usual setup where we have experienced no issues.

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