One possible reason for the payment failing is that your payment card has changed or expired. Pay the failed payment and update your card details with the following steps:
Sign into your Account
Go to Subscriptions (from the menu on the left side)
Open the order from the "view"-button
Scroll down to "related orders"
Find order number (#numbers) and click the "Pay"-button on the right.
You'll be directed to the checkout view, so please read and accept the terms & conditions and click "place order" button in order to pay the failed payment. After a successful payment your subscription will be activated again automatically.