You may need to sign out and sign in again on all AirDroid clients (Android and computer) so that the Premium will take effect.
You can check your account type by one of the following ways:
1. Sign in to AirDroid Windows/Mac, click the Account icon:
2. Sign in to web.airdroid.com, click Account and check the User type:
3. Open AirDroid on your device > Account and you may see the symbol of Premium on the upper left: