How do I add more sites to an existing plan?
If you have an active Akismet plan, you can add sites to it at any time by activating Akismet on the new site using your API key. You can cover an unlimited number of sites with a single Akismet plan. Because our subscriptions are capped per monthly API calls, you’ll want to make sure the total API calls made by your sites don’t exceed your tier.
If your API calls are exceeding your tier, you can upgrade your plan. Once you log in to your account and locate your Akismet Subscription under Purchases, click on the Upgrade link. This will add the next-highest tier of API calls per month to your cart.

You can also update your card on file here.
If you have trouble adding sites to your plan, or if you have any other questions, please contact support.