Click the top right corner in my Pingdom
Under the Organisation Settings (Appears for Owners and Admins) you can see your Subscription settings as well as all invoices. Direct link: https://my.pingdom.com/app/3/account/subscription
On this page, you can see your current subscription and make changes such as updating billing details or billing contact (will receive copies of invoices), change your billing cycle (monthly or annually).
Navigation Notice: When the APM Integrated Experience is enabled, Pingdom shares a common navigation and enhanced feature set with other integrated experience products. How you navigate Pingdom and access its features may vary from these instructions.