According to the pop-up message, your issue may relate to the difference in Apple ID for signing up and downloading. Please make sure that you signed up subscription by the Apple ID that you downloaded the app. To make it easier, please follow these steps:
1. Log in your iTunes by Apple ID that you used for signing up the app. (please find the subscription confirmation or invoice email from Apple to make sure you login by the right Apple ID).
2. Go to the setting -> Your name -> iTunes and App Store -> Tap to view your Apple ID -> Purchase history -> If you see the billing of our app in this Apple ID, please continue the next steps.
3. Tap Restore Purchase in setting. You can restore those purchases with your Apple ID login credentials without having to pay again.
4. Try to use Premium features. If it doesn’t work, please try to check the restrictions on your device to make sure in-app purchases are allowed or restart your device and try again.
If you need any help in advance, please try to contact Apple Support.