Hi, I am looking to add a button or option to the checkout, where customers can add a gift bag for an extra cost to their cart. I've been experimenting and decided that using the variant option is not ideal as it causes an error message, which could put off customers from buying. Instead I would like to let customers choose at checkout whether they would like the product to be sent to them with a gift bag. Any ideas (including coding as it seems there is not squarespace solution for this at the moment) would be greatly appreciated.