Hello Jane, thanks for joining the Community.
There's no feature for commission in QuickBooks Online, however, there are two ways that this can be recorded manually. The first would be to display this on the invoice by creating a product or service for commission and adding this as an item line.
If you don't want this to show on the invoice, you can instead create an expense account for the commission due in your Chart of accounts and then use the undeposited funds method. To do this, when receiving payment on the invoice, change the 'deposit to' account to 'undeposited funds' (this is a default account in QuickBooks Online used for holding transactions). After this, create a bank deposit (+ New > Bank deposit) and tick the payment under 'undeposited funds'. Check that the payment account and date are correct, and then scroll to 'add funds to this transaction' to enter the commission account (under 'account') and the amount as a minus fee (-).
