Enable Server Based SharePoint integration fails

I'm preparing two demo's and for both demo's I want to show the Office365 groups integration. To do this, I want to enable the Server based SharePoint integration, but that fails with the message:

Failed authentication

And the error:

<errorlog><sites>
  <site>
    <url>mod484719.sharepoint.com/.../crm&lt;/url>
    <exception>Object reference not set to an instance of an object.</exception>
    <errorcode>-2147088205</errorcode>
  </site>
</sites></errorlog>

I've been through alle online documentation I can find, but so far no success. There's also not much to configure. I did make sure that this user has the permissions on the SharePoint site collection.

As said, I'm preparing two demo's and it's the same for both.

Any ideas on how to solve this?