Free APIs (i.e API's with only free charges), are free to use. We take no fees from them.
PayPI charges fees on payments taken on the platform. PayPI takes 8% of the payment value and the rest will be transfered into your balance, minus any currency conversion fees.
Subscribers are charged £1 or $2 or €1.3 each month they make a request to a paid API depending on their currency.
For example, if a UK subscriber makes paid requests to two paid APIs in a month they will be charged £2. If the next month they make paid requests to only one paid API they will be charged £1 for that month. If they make requests to only free APIs, or free charges, they will be charged nothing.
If you have a charge for £0.01 per request and a subscriber makes 100 requests, totalling £1 of usage. PayPI will take 8% which is £0.08, leaving £0.92 which will be transfered into your balance and paid out at the next payout date (note this value does not account for currency conversion fees which may be applicable). The subscriber will be charged £1 for their usage (plus any applicable tax), along with a £1 processing fee for that month.