Welcome to the RankTank, it's awesome to have you on board, if you've made payment via Stripe then you'll have immediate access to the "Legacy" RankTank Google Sheets on RankTank.org, just use the API key received via email.
You can also now access the RankTank Google Sheet Add-On (you will have to subscribe separately using the Sidebar → Subscriptions menu on the right of the add-on) along with the other "Pro" SEO Tools if you are on a Major, General or “Legacy” Pro package. If you are unsure just drop us a message via email.
Important: First time RankTank users making payment via PayPal (for both the Add-On and “Legacy” Google Sheets) or via Stripe for the "Legacy" RankTank Google Sheets need to drop us a message via email with the transaction ID in order to be manually approved and issued with your API key and/or initial credit allocation.
You can follow and message our founder @Jaco_van_Wyk directly on Twitter should you require any assistance.