Apple Pay online

I use Apple Pay in the UK on my mobile successfully. I have tried to use Apple Pay on my iMac using Safari browser. The payment screen shows my correct debit card and detail but shows 'Invalid Shipping Address'. It won't accept my UK address. It appears to be validating against US addresses even though I am on a UK website as the suggestions that pop up when I am entering data are all US. It correctly finds my address from my Apple ID but doesn't like it.