Since originally releasing the app in the beginning of February I discovered that I have been misled concerning the storage of the receipt for the legacy subscription, subsequently I had to find a different way of handling users who have previously purchased the the V1 license key.
If you have the license key app installed and you purchased that license key from the Play Store in the past, then the app should recognize that fact and provide you with Pro access. Make sure that the old V1 license key is still installed on your device. Note that it must be installed from the play store, it cannot be side loaded.
If you continue to have a problem with this, please get in touch with me again.