Unsolvable compilation errors that show up as soon as Unity IAP package is imported.

Got it, so it’s not only 2019.33f1 for you (is what I meant). I am not familiar with an Android 12 issue. And correct, don’t use the Services window. You only import via Package Manager. I just used 2019.20f1 (because I already had it installed) and imported IAP 4.1.3 without issue. Then choose menu Services/In App Purchasing. However, don’t use an IAP Button or IAP Catalog, there are known issues with Codeless IAP. Instead, use Scripted IAP. I just published this updated Sample IAP Project https://discussions.unity.com/t/700293/4