expiration date gives error on test square up payment in sandbox mode

In live mode the payment goes through fine but am still testing so put it into sandbox mode for more tests. It gives me an error on the expiration date so can't submit, any idea as to why?

Have also tried with no info at all.

Following your screenshot, the reason that seems logical is that the year you have entered has already passed. By setting the expiration date January 2001 would simply mean the card is no longer valid.

If you have additional questions, please let us know.

Indeed. You are right of course. It was a very long night and head was clear. Thanks.