Google Play Billing.V2 subscription test fails


I’m trying to publish a new version which includes the new billing.v2 library for Google Play. I did the dropin changes as recommended in the documentation. However, when testing the build in the internal testing category on Google Play console, I get an error on the device log:
Corona : Error while purchasing because Product Id was not found

Is there a change I need to make perhaps due to Google moving subscriptions to the new model of Base Plan + offers? I thought that change was backwards compatible, but perhaps I need to modify the original product id sent to include some offer/base plan id?

In the console I see that my old subscriptions have been migrated to the new plan model. The product id remained as it was, but now there is a base plan id (called p1m) and another offer id (called freetrial).

Looking at the solar 2d document for billing.v2 (here), I see that the API still allows only a product identifier with no base plan/offer ids included, so I assume the library still uses the backward compatible version for launching a billing flow. So, I’m a bit puzzled as to what may cause this issue.