If you are a Self Serve Pay as you Go User, you can purchase more credits by clicking on the Buy Credits button
This will direct you to the Purchase One Off Credits Page, which will allow you to specify how many blocks of credits you want to purchase.
Please note that each quantity is a block of 100 credits
Once you have selected the number of credits you want to buy, click on the purchase credit button.
You will be directed to the payment processing page to enter your payment details.
Once you have completed the payment, you will be directed back to the subscription page, and your purchased credits will be reflected in your account.