If you don't currently have a PayAsYouGo Subscription, you will need to register.
In the top right-hand corner, click Register.
Fill in your details and in the Subscription drop-down. For now, leave it set to Pay Per Use.
You will receive an email confirming your registration. Click on the link to verify.
After logging in, click on your name in the top right-hand corner.
Then on the left panel, click on Subscriptions.
On the Subscription page, click Activate your Subscription.
Select your Subscription and then enter payment information.
When you sign up for a subscription, your first payment will be charged immediately. Then it will be automatically renewed on this same day every month that follows, until you cancel your subscription.