A payment for post purchase offers can fail in some cases (for example: insufficient funds, CC errors, etc).

If customers accept an offer but runs into a payment failure, they will be directed to the thank you page and prompted to enter payment again to accept the post-purchase offer.

In addition, customers will receive an email from Shopify letting them know payment is needed to complete the order.

On your orders list, the order will show as a partially paid order. To handle the situation, you can potentially:

* Collect the payment (through the checkout link Shopify provides)

* Edit the order manually to remove the unpaid item

* Refund the order

Another possible reason for a partially paid order is capturing payments manually.

In this case, a payment must be manually captured for the original order as well as any post-purchase offers before the order status will update to paid.