Domain Mapping – purchase domain eNom brings "Are you sure you want to do this?" error loo

Dear Experts

Unfortunately something is broken, when I would like to use the purchase domain function in Domain Mapping, I recieve “Are you sure you want to do this? Please try again.” error loop.

Searched in internet and already tried to deactivate all plugins (except domain mapping and multi sites of course, otherwise purchasing domain shouldn’t be available anyway) and also tried to swith theme to standard theme (twenty sixteen), but the problem persists.

Would it be possible that this may be caused by the wp-config.php somehow? I did not really change something there. Really means, i did, but only pushing define sunrise more to top, but it didn’t help and i pushed it back where it was before, so no real change.

I have re-activated the plugins but I would appreciate your help.

Any Ideas what I could try?

Kind Regards,

Manuel Fernandez