Step 1: Sign into your developer account console HERE

Step 2: Upon signing in with your credentials,  you will see a dashboard listing your  Apps.

Step 3:  Click on the App for which you'd like to subscribe to a Paid Plan and choose the "App:Billing" tab.

Step 4: Click on the SUBSCRIBE button of your chosen plan and fill in your credit card details.

Step 5:  After entering valid credit card details, click on the 'SUBSCRIBE' button and confirm your plan selection.

You should see a message confirming your subscription. A confirmation with a receipt will also be sent directly to the email address associated with your account.

Other articles you may be interested in: Can I pay by invoice instead of by credit card?| What are Peer Connections and how are they measured?| How is TURN Bandwidth measured and billed?| How is MCU/SFU Bandwidth measured and billed?| What happens when I exceed the included amount of Peer Connections or Bandwidth in my plan?