Android Pay uses your Android device to make contactless transactions, so you don't need a contactless-enabled debit or credit card to use the service.
Contactless payments using an enabled debit or credit card are subject to a limit per transaction, which is currently set at up to £30 in the UK.
Android Pay contactless transactions using your Android device have no such limit. This is because you authorise Android Pay payments over £30 using the fingerprint sensor, your PIN, password or pattern, increasing the security over standard contactless transactions. However, merchants may have a limit set on their terminal, and you should have the available balance and credit limit to make the payment.
In-app transactions are also limitless: as long as you have the available balance or credit limit, the transaction should be authorised.