Is there a way to find out why certain contactless transactions get declined but go through ok with the pin? Most recent one was for £3.48 which is a trivial amount.
Depends on the country where you pay. I live in the Netherlands, if I have done several contactless payments for a total of 48 euro in a row and my next payment is 3,48 euro, then I have to use pin and chip for that payment.
Check this (under floor limit):
For the UK (you were talking about payments in pounds) I also found this here:
"Is there a daily limit on how much you can pay on contactless?
There is no daily cap on the number of individual transactions you can make (each up to £30), but occasionally, as an extra security measure, you’ll be asked to enter your PIN to verify you are the account holder."
My Amex gets declined very often at certain purchase points for contactless and is accepted with the same terminal as pin & chip, as are contactless payments with other cards. The error message is different from the “please use pin”. Haven’t had a good explanation, somehow it seems Amex contactless has to be activated separately by the merchant or processor.