They weren't very specific - there was a list of 6 or 7 possible reasons why it was refused. I'll have to check with my wife as it was her email account.
They are a US company but have a registered UK Address on Companies House.
I tried the chargeback but the bank said there was a 13 month limit - seems harsh on gig tickets in Covid times. It was Debit card if that makes a difference. The link seems to say 120 days limit.