Same issue: Error 43881 when trying to set up new tenant (and subsequently buy licenses).
Same issue: When attempting to purchase licenses, we got this error message:
Please try again in a few minutes. We are unable to complete the verification check on your payment method at this time. (CV: pr+0aAAAa0AAAAAA.16)
Solution: We called MS Support and they created a sales quote for us and emailed us this link (sanitised here):
https://signup.microsoft.com/get-started/quote?salesquoteid=aa0000a0-aaa0-00a0-0000-a000aaaa0000&ali=1&bac=1&signedinuser=username%40domain.com.au (Note: the %40 is code for @ symbol - so make sure you use that format in your URL when entering the details of a user account already active.)
Then we were able to proceed with the purchase (and overcome the 'payment method validation' issue).
Very frustrating time-waster. Not entirely sure how the Microsoft back-end systems failed to validate the new business tenant's payment method. And their did not seem to be any steps/instructions to troubleshoot this ourselves (i.e. a portal page to manually remediate the validation issue).