Can I issue my guest an additional payment link after the reservation is paid in full?

Yes. Open the reservation and click Send a payment request in the Actions panel.

In the popup, under What is this charge for?, choose Extra service / fee - a side charge for things like a pet fee, damage or a late checkout, which does not affect the reservation balance. Enter the amount and a description, then send the link to your guest.

The option beside it, Partial balance payment, is greyed out once a reservation is paid in full - there is no balance left for it to apply money to. That restriction does not apply to the extra charge, which you can send whatever the balance is.

You can also choose how to collect it: charge the card straight away, or place a hold and capture it later.

The Send a payment request button appears once you have a working connected payment processor on the listing, so if you do not see it, check Connected Payments first.