Paying an outstanding amount in Customer Portal
If your customers' change to their order results in an outstanding amount, they'll be able to get redirected to the checkout page to pay the balance due.
Balance due after edits
If a balance is due after your customers save their order changes, a banner will let your customers know that a payment is needed.
When your customers click the Pay Now button, they'll be redirected to the checkout page.
Note: Your customers will also receive an email notification with a checkout link to pay the amount due on their order.
If your customer doesn't pay the amount due in the editing time window you selected, you can resend an invoice for this order through your Shopify admin.