The most common reason for this issue is an error received from the Google Play API:
“Google Play Android Developer API has not been used in the project before or it is disabled. Enable it by visiting the Google Play Console.”
To resolve this issue, please ensure that the Google Play Android Developer API is enabled for your project. Once you’ve done that, try testing your purchases again. If the problem persists, consult the Qonversion documentation or contact support for further assistance.