When using an email address on an exchange server via owl to validate a license there is an error message that the email cannot be found and license validation fails unfortunately. So far I was able to reproduce the bug on Thunderbird 128.
Unfortunately there is currently no other workaround than using an account that has a different server access method (such as IMAP or POP3).
This is caused by a bug in the accounts extension API. The malfunctioning API called is accounts.list()
https://webextension-api.thunderbird.net/en/stable/accounts.html#list-includesubfolders
I have raised a bug with Mozilla to handle this:
https://bugzilla.mozilla.org/show_bug.cgi?id=1909005
Thunderbird core team has already made a patch and are currently testing this with Thunderbird 131 (as of 10/Aug/2024).