To subscribe, just follow the easy steps below:

1) Go to the menu located at the upper right corner of the screen. 

2) Tap "Account".

3) Tap "Upgrade" button under subscription.

4) If you have an existing credit card (payment method) enrolled in Google Play, tap on Subscribe.

5) If you wish to use a different card, tap on ">" icon.

6) Enter the new credit/debit card details then tap "Subscribe".

7) Once payment is successful, Google Play will ask you if you want to require authentication for purchases to be made on the device. Tick “Yes, always” if you wish to require authentication for purchases. Google Play will ask you to enter your Gmail password or enroll a fingerprint for all in-app purchases to be made on this device. 

 NOTE: If you have previously set authentication for purchases in Google Play, just enter your password or fingerprint.

 8) Click verify to proceed with the payment using the enrolled card.

You will receive an email confirmation that you have made a subscription from iWantTFC via Google Play.