Some problems in the UK with Apple Pay - my payment was rejected by my Bank for some reason - tried another card and this was then rejected on the website as well.
I contacted Apple and apparently some Banks refuse large(?) amounts through Apple Pay but, then Apple's system can't purge that payment from their system for a new payment method to go through.
I had to cancel an order from January 26th and order again - delivery is still February 9th however.
I had the same issue.
I first called the credit card-issuing bank, who said the failure was not a fraud-check block (like some large / unusual pattern transactions lead to).
They advised trying the payment again, manually entering the card details instead of using Apple Pay.
The Apple order page allowed me to do this, but the payment was still not authorised.
I then tried the option of using a different payment method. This also failed, with a totally different credit card immediately not being authorised.
So at this point I guessed it was not likely a payment problem, but an Apple / Apple Pay problem, and contacted Apple.
When I described the problem, they said that the re-attempt can fail and is a known issue. They said that their website doesn't properly clear the previous payment details, leading to the re-attempt / alternative payment method to appear to fail. Apple stated that they are able to put the payment through using their systems. True to their word, after giving my original payment details and Apple applying them to my order manually, the payment went through OK.
Just describing my experience in the hope that it will help someone in a similar situation. Re-ordering may not be necessary - a call to Apple may be all that's required. (Could be particularly useful on a future product order where a re-order might lead to being put to the back of a long queue.)