Cannot connect to your server... Failed to receive challenge... Here are some tips!

enable-query=true
query.port=25565

Need to be placed in the server.properties file on your server...
If you are using bungee-cord do the equivalent in its setup files.

Rest assure this is not our error, but it is yours. If your server is running of a host please tell them your problems, they may be able to help you, If you run your server independently, add me on Skype and we will figure it out together.