I try to go on a server but it says 'Cannot have username longer than 16 characters only'

I try to go on a server but it says 'less than 16 characters only'

*What I expected to happen was that the game would connect me to a server

*What actually happened was the screen said 'Cannot have username longer than 16 characters

Steps to Reproduce:
1.Log in
2. Press Multiplayer
3.Go on a server
4.It should say 'Cannot have username longer than 16 characters'