Hi @Jon_Smith
Thank you for your suggestion - it worked 
Initially I only had the basic URL for our on-prem Orchestrator, but when adding the entire URL, including the ID-part, it worked.
It is quite a unique scenario/requirement.
It is for a live demo at a conference, where I would like to use Document Understanding, but base its contents (documents) on data that our participants can relate to.
This data is fetched through API-calls to a digital document platform, for which we have made several libraries (on the on-prem), and I would like to show them how easy they can build something that works.
By combining the two tenants, I can showcase “new” features, but do so with libraries that are already available to all our developers/citizen developers.
Regards
Soren