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This would mean that the app you're posting from has no post authority, meaning you have not authorised it to post for you, or you have not provided a valid posting key for your own account (to the Hive Keychain, for example). You posted a comment, which requires post authority. Use the same app and you'll be able to post.

This was not the case. I posted this comment from the same place as I tried to post the piece. After this issue, without me doing anything, and after a few times I tried to do it again, I published the article. HOWEVER :-D, once I wanted to edit it, I once again couldn't do it because of another issue (I don't remember what it was). Anyhow, I hope these things can be resolved ;-)