1. Multiple Google Play Accounts
Google has a policy that only checks one Google account (the primary one) on your phone for pro purchases. If you have multiple accounts on your phone, Google Play may be checking the wrong account for your Flowx purchase.
This issue has been discussed to death since 2016 here: Play Billing Issues. Unfortunately, Google doesn't seem to be addressing this.
Go to Android Settings > Accounts > Google to check how many Google accounts you have on your phone.
If you do have multiple accounts that is causing this problem, you can follow the instructions given by a Flowx user with two Google accounts:
- Delete the Flowx app
- Remove the business account (I bought the subscription with my private one)
- Clear app data and cache from the Google play app and the Google play services
- Reinstall flowx with the right account
- Restart phone
- Add back the business account
Sorry about this problem. I would rather not have it but I cannot do much about it.