The permission to transfer ownership or update payment method is granted only to the role of Site Owner. You can see who is assigned the role of Site Owner by clicking Team in the Site Dashboard or Professional Workspace. Other roles do not have access to billing as described on this page.
Refer to Change Site Ownership for instructions.
You'll receive an email inviting you to pay for the site when a Supporting Workspace is ready to transfer ownership of the site to you.
If you already have a Pantheon, log in to that account before you begin. If you're not logged in, you'll be prompted to create a new account.
Open the email and click Make Payment.
Select an existing card if one is on file, or add a new card to use as payment for the site.
You will receive invoices at the end of each billing cycle after you've accepted the invitation.