Power BI Embed on AppOwnsData scenario Dynamic Binding does not work

Following the documentation at:
https://docs.microsoft.com/en-us/javascript/api/overview/powerbi/bind-report-datasets

I created a report that connects to Database A.
I cloned the report and connected it to Database B.

Both are identical (except for data).

Both are added to Azure on the same account, same permissions.

I can use the sample from https://github.com/microsoft/PowerBI-Developer-Samples/tree/master/.NET%20Core/Embed%20for%20your%20customers
and connect to both.

But when I try to use dynamic binding and make report A connect to Dataset B, it doesn't work. It either opens the original dataset if I leave the dataset id on the token request, or nothing shows up if I omit it.

I am sending both dataset IDs to the token request.

Even setting the id on the javascript options as the documentation above mentions, it doesn't work.

Apparently there's an 403 error.