Scenario: The user is trying to rent a car using an application but the credit card on file has expired.
Challenge: Write them an error message so that they can correct the problem.
Headline: 30 characters
Body: 45 characters max
Please input another card's details.
Originally I had it as 'Your Card Is Expired', but have changed it to 'that.' It makes it sound less of an emergency or error that way.
With not a lot of characters to use for the body text, it was either an instruction or a more detailed explanation of the headline. I went for the instruction. Either the user will bang in a new card, or they will have leave and not rent the car. This instruction gets the user to that point, in a hopefully compassionate way.