For that error msg i would also wonder if the OU already exists.
Your existing OU isn't in the same place with the same name as SolidCP is configured to create right?

no, the new OU is on a different OU than before. Like in your video. I've also tried to do it in the same OU than before but this was also not working. And I've tried to rename the old OU before creating the new one. Nothing was working.
My database is completly empty. When I show the top 1000 rows of the domain table, the query is empty as expected.

any system objects such as the security group / Public Folder user?
alternatively you can manually create the org by not selecting the automatic provisioning checkbox, then go to organizations --> add organization, give it a unique ID and good name --> select the domain you wanted to add and see how that goes

Yes, this is a question for me too. I have for every of my organizations a security group and a public folder mailbox user. How to proceed with them. I've seen that you unchecked this users when you import.
Are they the reason why I couldn't create my hosting space?
big confusion for me...

Well it's falling over something that it doesn't expect to be present.
i know for sure that it doesn't fall over "Accepted domains" (i tested this) they can exist already and SCP continues creating without issue.

i never tried security groups or PF users that are identical to what it's trying to create. so that would be something you can try out

For me, it's clear now that the organization id is failing over the existing security group in AD. But even if I change the name of the existing security group, it's crashing. Perhaps another ad attribute is causing the prob.
I'll keep you posted when I've found something...