When setting up your Play Store service credentials, it can take up to 36hrs+ for your credentials to work properly with the Android Developer API. You will see "Invalid Play Store credentials" errors and be unable to make purchases with RevenueCat until this happens. Any changes to these credentials will also take up to 36hrs+ to fully propagate. If the Google Play Android Developer API has not been used in your project before or it is disabled, you can enable it by visiting APIs & Services in your Google Cloud Platform.
Service Credentials Not Populating under API access
This is a rare case, if your service credentials are not populating under Google Play Console > 'API access', be sure to check if the service credential email address is in the "IAM" tab in Google Cloud Console. To navigate to this page, go to Google Cloud Console > IAM & Admin.
If you do not see your service credentials under this tab, select the "+ ADD" button at the top of the page and copy the email from 'Service Accounts' tab. Be sure to add the 'Pub/Sub Admin' and 'Monitoring Viewer' roles.
After saving, you can return to your 'API access' page and 'Refresh service accounts' to see your service credentials.