Hi @edme
First of all I am sorry that we did not manage to reply to you before, I did reply to you a few minutes ago on discord, I hope you will get to see at least one of the two replies.
The most common problem about not being able to post is a wrong posting key.
Please see the video to understand how to find your private posting key:
Let me know if it works out well for you. Sometimes it might need to be written manually because when you copy-paste, you may copy a 'space'.
If this does not work, do not hesitate to ask me again here or on discord.
Hoping to see you actifitting!