I had the same issue for our organization in Switzerland!
But I finally managed to submit the form with these inputs:
- I used the “Tax Id” and not the “Duns Number”.
- The swiss business UID register let's you search for your company. Once you've got your tax number, in our case in the swiss format
CHE-104.079.670
, you have to retype it without hyphens or dots, and with the ISO country code (3 chars) as prefix:CHE104079670
This passed the validation successfully and we received the e-mail validation step just after it.