Hello, thanks for the investigation. I believe I have exactly the same issue (embed works for existing topic but fails at topic creation). This works on my production environment but not on my dev machine.
My setup is a docker stack, and I made sure everything is visible from both discourse and sidekiq. At this point, I’m starting to think that when Discourse tries to parse a URL (it also fails when onebox tries to pull a preview of a link in a post), it somehow depends on an external service that fails to see local instances… Would that be possible ?
@wilson29thid did you find anything on your side since then ?