Can't test subscription upgrade/downgrade. iOS doesn't use the sandbox account

Hi,
I am trying to test my subscription upgrade/downgrade path on a device. I added a test user to the sandbox section of Settings -> App Store and can purchase subscriptions using that test user no problem in my app.

However, if I click on "Manage" on the sandbox user to see the list of subscriptions, when I try to upgrade/downgrade the purchase UI that iOS shows tries to use my actual personal account instead of the sandbox user, so I can't complete the transaction.

Looks like a bug in the sandbox testing flow in iOS, but any way around it? Right now I just simulate updates from apple on my backend to make sure my app behaves as expected, but I would like to actually get some "real" data from Apple.
As long as the payment sheet says [Environment: Sandbox], you can use your regular Apple ID and not be charged. The receipts are still tagged as coming from the Sandbox environment.
Unfortunately, entering my real apple ID/password does not work. It show success but the upgrade/downgrade never occurs the UI still shows the original subscription level.

Signing out of the production AppleID and only having the sandbox tester on the device doesn't work either. In that scenario the password box is displayed but with an empty username in the dialog, entering the sandbox password just fails.

I'm confused how people are successfully testing these scenarios :/
Has anybody found solution for this? I am facing the same issue
I try to simulate the downgrade by purchasing the item from within my app.

This appears to work however the receipt still shows that the expiration date is unchanged for the original purchase and so I am showing both subscriptions ACTIVE despite the fact you can only have one active at a time.

Looking at the subscriptions from the settings/sandbox area, this appears correct. Really wish I had confidence in this process but I don't. And cancellation date always shows empty so can't count on that either.
Can't test subscription upgrade/downgrade. iOS doesn't use the sandbox account
 
 
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