hello i am facing the same problem , my IAP button does not work
i have followed this link :-Unity - Manual: Codeless IAP
i have done all the step shown in this link and some that are not shown in this link like
i imported iap plugin and fill in the google play key it needed
i have created IAP catalog and buttons perfectly and linked it with the script storeHandler (handle when onPurchaseComplete and failed)
then i exported google CSV file , and then i exported the project as .aab(<-playstore file not apk)
then i uploaded csv and .aab file to my google play console as an internal test (alpha test ) and register my email as a tester in google
after google publish my game , i downloded it from the link it generated for internal tester and there i see a failure reson → PURCHASE UNAVAILABLE