The Pro Pass is a Subscription, which means it will grant you perks for as long as it's active in your account. It also means that it will renew automatically, so here are something you should know about it:

How can I buy the Pro Pass?

You can only purchase a subscription if there is a in-date credit card on file in your account. A credit card is needed because the subscription will be recurrently charged.
Unfortunately, App Store, iTunes, and Google Play Cards are not valid payment methods for subscriptions. If you have any doubts regarding accepted payment methods, please contact the app stores directly.

How does the Pro Pass renewal work?

When you acquire a subscription or a free trial, a pop-up message is displayed by the respective store informing the current value and stating that the subscription will be  automatically renewed after that period, even after the app is deleted. The subscription will charge your account upon each renewal, and to avoid being charged you must cancel the subscription.

How can I cancel the Pro Pass?

Subscriptions are directly linked to the account you use in Apple’s App Store and/or Google’s Play Store. This means that the subscriptions are linked to your account, and not to the game itself, and that we are unable to cancel it remotely.
So, in order to cancel your subscription, you must access your account and terminate your membership.