If a customer has picked up their order, mark it as complete by following these steps:
1. Go to All Orders.
2. Select the order you want to tag as complete.
3. Tap Complete Order.
To share the invoice to your buyer/customer, tap Copy Invoice Link.

If you are unable to see the Complete Order button for Customer Pickup orders, this is because the order has not been paid for yet. You may follow up payment with your buyer and, once paid, you should be able to see the Complete Order button appear.