The standard Goods & Services fee applies to a normal commercial payment, a percentage of the transaction plus a flat amount, taken out before the funds settle into your balance. It's the same structure whether the payment came through a checkout button, an API call, or an invoice, since PayPal treats all three the same way once money has actually changed hands for something.
Friends & Family skips that fee when the sender funds it from their own PayPal balance or a linked bank account, which is the whole reason it exists as an option. Funding it with a card, or sending it across borders, usually brings a fee back into the picture even on a Friends & Family payment, along with a currency conversion markup on anything that crosses currencies.
A dispute that escalates into a chargeback through the card network, rather than staying inside PayPal's own Resolution Center, can carry its own separate chargeback fee on top of whatever the original transaction already cost, which is part of why keeping a dispute from escalating that far is worth more than just the refunded amount.
Rates and exact numbers change more than once a year and vary by country and account type, so check your account's current fee schedule directly rather than relying on a percentage that might already be out of date.