Our Website hidden link Plugin does not accept they Key to connect to our Account.
We have also deleted the site on WPML Account and added new one and generated a new Key.
It still not work.
Key has been insert by using copy/paste function.
Please go here (https://wpml.org/account/sites/), remove the old site, generate a new key for this exact domain (hidden link - see that we don't add the "www" anymore), then copy the key, then go to your WordPress backend > Plugins > Add new > Commercial > and register WMPL.
That should work.
I hope that you will find this information helpful!