Please contact you payment provider if you encounter problems with completing orders.
If you have recently integrated Quickpay and set up a payment provider agreement. It can take some time before your payment provider agreement goes through and is ready to use.
Another common isssus with completing orders are offen associated with exceeding the payment providers time limit.
This means the reason you can't complete an order is propperly because you have exceed the time limit of completing orders.
The different payment providers have different time limits.
With Stripe as your payment provider you have 7 days to complete and order. If you exceed this time you won't be able to complete the order.
With Quickpay as your payment provider you have 30 days to complete an order. If you exceed this time you won't be able to complete the order.
Read more about the diffrent payment providers time limits here.