invalid_tenant when exchanging Auth Code

[SitterIT]

Have en web app like this:

Pasting in the grant url into the browser:

And get the auth page up: 

I also receive the auth code:

But when doing the POST https://connect.visma.com/connect/token I get error 400 - invalid_tenant

Looking in the dev portal, no customer has been added.

I've also tried with different users, all having the Integration Admin setting in 

[SitterIT · Accepted solution]

found out of it. user also need to have api_user also.