Gitlab Dashboard Widget throw an error

I’ve installed the Gitlab Widget on Dashboard, enter my Gitlab access-token (non self hosted gitlab) and it shows that it was successfull in the settings:

But If I open the Dashboard, I see an error in the dev-console:

And If I follow the link <domainname>/apps/integration_gitlab/todos (open it in new Browsertab) I see this:

I do use a managed nextcloud service from
Any Idea what the issue here might be?