Where at check out does a customer enter the Party Code?

When the Affiliate gives the customer the Party Code for the Party where does the customer enter the code?

Glad you asked this. Same issue. BTW - figured I’d ask another Shopify user - any good Shopify events you got your eye on? I’m looking that this one https://ecomlivestream.com. Free and a nice lineup of speakers (CoFounders of $1bn+ brands). Any one have anything else on their radar? Are you part of any other communities. I’m new to Shopify ecosystem and looking to network.