i am newbie to this mining

i have a L3+ and i have tried yesterday to set it up to mine with prohashing.com
i have set the server to the prohashing serve
http://prohashing.com:3333/
i have added my user name
and left the password as blank,
however yesterday when i applied the settings , in the settings of the miner it was showing as DEAD and automatically switched to the second pool on nicehash,
did i do something wrong or was the server down?
thank you