Wizard for server-based SharePoint integration shows wrong "default" URL

Setting up the server-based Sharepoint (online) integration for Dynamics 365 for sales (online) is an easy task: just start the wizard :-)

( Description: https://community.dynamics.com/crm/b/magnetismsolutionscrmblog/archive/2017/12/19/setting-up-server-based-sharepoint-integration-for-dynamics-365-online)

Unfortunatly I had the following issue: 

After starting the wizard an comming to the step where  you see the dialog for the Sharepoint URL

there was shown a wrong URL and no chance to change this. 

(the picture below is just an examle of this step - in my "version" I could not enter data in this step!!)

There was no setup of any URL in Document Management before, there is no other Sharepoint integration or anything else.

With my user credentials I was not logged in to another Sharepoint site (afaik).

I found a solution but now I'm asking myself if there isn't any official or "correct" way for this.

This is what I did:

Start creating a new document site (1) , click on the link to the "default" site (2) and changing the wrong URL (3)

Then save changes to the default site and leave the "new document location" without saving.

This solved my problem. After restart the wizard it shows the correct site and the rest was fine...

My questions now:

• - how gets the wizard the URL without any (known) setups before and 
• - why was it not possible to change the site URL within the wizars
• - ist there a correct/ official way to solve this problem?

KR

Marc