Of course you don’t have to pay for the items you sent back! You just need to pay for the things you kept, plus the invoice fee, the shipping fee and the return fee. If you didn’t keep anything then you only need to pay the return fee.
Remember to pay the invoice in time, even if your return hasn’t come in yet. If it’s not paid in time, then any additional reminder fees can’t be removed! You can use the payment details on the original invoice to make the payment.
Pro tip: Register your return at AfterPay through the AfterPay app, so your due date will be moved back by 10 days – pretty nice, no?