As per [this]( Unity IAP package 4.12.2 is now available page-2#post-8955147) post, they updated to v5 in 4.8.0.
- Google Play - Billing Library update from version 4.0.0 to 5.1.0 [Google Release Notes](https://developer.android.com/google/play/billing/release-notes). New Google Billing features are not supported yet, they will be included in a future major update.
Proceed downloading that version and try to put it back in 2019.4. We will see what issues exist and try to fix. Most likely there won’t be any android side issues. Even if issues exists, it’s solvable!