Thanks eltutz -- The Offtiktok website was never very good with profile pages and I am getting a 404 page for profiles as well. However it still appears to work for me with video links. I have amended the Add-ons description to specify it works for video URL's.

UPDATED 2/18/26: I've updated the Add-On to use UrleBird instead. Unfortunately it can only be used on profile pages at the moment. Hopefully better solutions will be found and I can add more functionality. The issues you saw were at the onset of the decline of Offtiktok. Both it and ProxiTok no longer work and their projects appear dead.