That's most likely your code's problem. Please check again.

Return breaks it out of the for loop and returns the result. That means it will only loop once and look at the first character in the sequence. You can see this if you print out your c variable. The return statement needs to be after the loop has finished to check every position in the postcode. The tests you are passing are only because your code always returning false and will pass for any tests if false is the answer. Please mark this as a question and not an issue next time.