Assigning License failed

Hello,
As described in the link, we wanted to convert our 3 websites to the purchased premium version.
The license ist assigned to ….Do you confirm? Yes/No
Unfortunately, the error message appears for each domain:
cURL error 28: “Resolving time out after 5515 milliseconds”

What’s going wrong?

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