Have you tried debugging your client code to see what strings it receives? Add a println() fto show receivedMessage after:
receivedMessage = input.readLine();
Likewise on the server, display ALL the traffic.
A suggestion:
Instead of entering command strings separately in each program (
you may type them differently any time), define them as constants (static) in one place and use the variable names in your code. Then you can be sure they are all referencing the same value for a String or whatever type the variable is.