Command Line Interface

Can someone point me in the right direction for the CLI to set the volume of a player to a specific volume level using a get command. I tried the following from my browser to set volume on the player to 50 but doesn't work:

'http://IP_ADRESS:PORT/anyurl?p0=listen&p1=mixer%20volume=50&player=XX:XX :XX:XX:XX:XX'

Any ideas on the correct command syntax?