post {protocol}://api.ws.sonos.com/control/api/{version}/groups//playback/lineIn
Use the loadLineIn command in the playback namespace to change the current group source to the line-in source of a specified player. This can be be any player in the household that supports line-in. See Using Line-In on Sonos on the Sonos Support site for more details about the line-in capabilities of our players.
You can tell whether a player has line-in capabilities with the LINE_IN value in the capabilities object. See the groups object for details.
The player will switch away from the line-in source when the hardware detects that the user has physically unplugged the line-in cable.