The amount the developer is taking as a fee for facilitating the payment on behalf
of the seller.
The amount cannot be more than 90% of the total amount of the payment.
The amount must be specified in the smallest denomination of the applicable currency (for example, US dollar amounts are specified in cents). For more information, see Working with Monetary Amounts.
The fee currency code must match the currency associated with the seller that is accepting the payment. The application must be from a developer account in the same country and using the same currency code as the seller.
For more information about the application fee scenario, see Take Payments and Collect Fees.
To set this field, PAYMENTS_WRITE_ADDITIONAL_RECIPIENTS OAuth permission is required. For more information, see Permissions.