Why is my BMW digital key card not working?

You're first going to want to inspect the key to see if there is any damage to it. If it's not damaged then it's possible that it has been deactivated. You'll want to go into the vehicle and look at it's settings to see if the key is still running and active. The sensor that recognizes the key may have gone bad and this will need to be determined by a scanner tool. If You don't have access to a scanner tool then You might want to take it in to Your local dealership so they can have a look at it.