When attempting to add a mastodon proof in the client I enter my mastodon.social username with proper capitalization:

When I click on Authorize I'm greeted with the following error (Cannot create a proof for eeems while logged in as Eeems. Log in as eeems and try again.):

thanks! we have already fixed this actually. it should be in the next mastodon release. sit tight and try again soon. :)
@xgess _but I want my proof now!!!11_
Jokes aside, thanks for the quick response!
Edit: Any chance you could link the PR that resolves this for traceability? I'm having trouble finding it.
Can confirm that it now works. Thanks again @xgess