You are charged for your API usage at the end of each month. For any month that you use an API you are charged 20p + the cost of your API usage.
If you have used a free API or only free charges of an API you are not charged at all for your usage (this includes the 20p monthly fee)
Your Subscription Secret which is used to make requests to the API is shown on the subscription page of the API. Documentation can be found on the website of the API Partner (if this is not present and clear, please report this to [email protected])
To add a payment method to a Team, go to the Team settings by clicking on the icon in the Teams menu.
Showing Teams menu
When in the Team settings, go to the Billing tab and select "Update payment method" to change or add a payment method.