After 1 month trying to get my trial account working, having the chat support saying that couldn’t help me, the email support that didn’t help either and didn’t reply but once, saying they’d grab some info about my account and get in touch but they never did…
I asked a friend to open an account for me and it worked like a charm in less than 15 minutes.
Then I tried to install Discourse and I struggled a lot. I followed the Oracle Discourse installation tutorial but for some reasons, I couldn’t connect to the port 443.
I tried installing Discourse on a regular Ubuntu image, but I couldn’t get connect through port 80 nor 443 for unknown reasons.
I went back to the official instructions, it wouldn’t work at first (both ports connection failed), but I restarted docker and then it magically connected to both port.
So my experience isn’t the best, whether the issues comes from me or Oracle.
But in the end, I do now have a free, online, obviously not the fastest, but working Discourse installation. 
For those who want to follow the same tutorial, there is a small mistake in the server firewall part.
Instead of:
sudo firewall-cmd —reload
You must write:
sudo firewall-cmd --reload