Log into OnFrontiers at https://onfrontiers.com/login
Go to the Team tab > and click the gear logo for Team Settings
Click the Credits section on the left of the page
Select the number of credits, see discount & total amount. Here's a reference on how many credits to buy.
If no card is available on file, you'll be prompted to add one
We'll promptly charge your card or bank, load the credits to your account, and email you a receipt