Apple Pay won't confirm purchase

[xetmarcr]

The website shows a 'Pay with Apple Pay' button, and both devices (Macbook & iPhone) are signed on with the same Apple ID. However, when I try to complete the order using my iPhone as I would with an in-person purchase, a message appears on the computer screen something like this:

'null' is not found to complete transaction

I have used the Apple Pay feature successfully several times with in-person purchases but this is my first attempt to purchase online with Apple Pay.

Anybody know what may be the cause of that message?

Thanks in advance.

 

[AdamC301]

A couple of days ago, I tried to check out of an online store with the "Pay with Apple Pay" button. I was using my iPhone and this was my first time using "Pay with Apple Pay". The transaction did not go through, was canceled, and the message that popped up said something like "Too many attempts to complete this transaction".

I logged into credit card account to make sure the issuer didn't have anything blocked or flagged, and everything was fine.

I am to puzzled by this.