Had the same problem until I realized that this is not about beta or not. For me, it was about switching from IAB v2 to v3. In particular, accounts added to “Play Console”> “Settings”> “Account Information”> Gmail accounts with test access. I had accounts there long before alpha / beta appeared. After deletion them + 3 hours or so for distribution, the test message stops displaying.
Perhaps the documentation will be recorded in the v3 in-app billing, but I have not seen it.
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