The Billing page can be found in the top main menu bar, next to Settings. From this page you can purchase and manage your Tallyfor subscription.
Use the Purchase a Subscription buttons to be taken to a checkout where you can enter your credit card or ACH information. You can add Additional Returns to your subscription during the checkout process.
The checkout form.
To learn more about Tallyfor subscriptions:
From the Billing page, you can also see how many ATB's you have available and review the ATB's you have used. You can also manage you subscription.