We are so sorry to tell you: Out of Milk Pro is disabled right now.
If you bought the Pro version - you can still use it like before. You should not see any ads, as long as you are still using an Android device. Your Pro subscription should follow you to any new Android device as well - it's linked to your account.
Sadly you can't buy Pro at the moment as a new user. While we are working on a business model that will allow us to offer Pro again in the future, for now it isn't possible.