There may be several reasons why the subscription code doesn't work. Check as follows:
1. Fill in the correct subscription code.
2. If still with problem, check whether the correct VERSION of APK is installed.
There are two versions: Standard(Blue color), Plus (Red color), they are using different free trial code.
3. If you have purchased the wrong version subscription code, please contact us to replace.
If you change subscription code from Standard version to Plus, It is OK and please contact us. And you can pay the balance if any.
Please pay attenton: do please not activate the code, if you want to change/replace.
4. If the above methods do not help, please contact our support email directly.