I ordered a new "Microsoft 365 Business Premium" license yesterday morning and also received error code 43881. In the admin portal I noticed that everything looks fine, but no license can be added.
Then I called support and had a very rude lady on the phone, who gave me the ticket number 2311010040002922 and said that someone from technical support would get back to me in 1-24 hours, which of course did not happen. This is really a very unsatisfactory situation, apparently Microsoft does not need to get new customers.