Azure now Entra. Plus docs unclear about adding permissions

[Brantone]

Followed README to the letter.
Continually got "404" for a product Id I'm staring at.

Tried to go into PartnerCenter to see if changing permissions would affect anything.
Now locked into having to update "Reply URL" and "App ID URI" - neither of which should be applicable, but not able to due to requirement.

All other pre-requisites are satisfied.

Additionally: not clear if the 404 error is result of some misconfiguration (have confirmed App has access to "Publishing" for the product), or something else?

[Brantone]

Further information:
README says has to have R/W on "Publishing" --> was able to get some response with standard "Developer".

However: only applicable to our Xbox app, not UWP app. Still getting 403 error.
The docs do state Can I use one Azure app name for multiple products ; but wonder: is it a "one and done registered" or is testing multiple even allowed?

Oh - also - bigId is the "sort of product" id? .. URLs in PartnerCenter have it https://partner.microsoft.com/en-us/dashboard/products/BIGFAKEIDTHING/overview ... but even if it's after products, it's not productId. This is further confused by a seemingly shortage of other info on bigId ... or just me??