When you create additional fees per account or per listing, you choose which booking channel and payment they should apply to. Focusing on the payment aspect, when you configure an additional fee to be a percentage fee, you must also decide how that percentage is calculated.
For example, if you want to charge 5% for an additional bed, that can be 5% of one of the following:
"Entire payout" is the total of the accommodation fare and cleaning fare. It does not include taxes or any other additional fees.