The above described API is for Music Cast devices, your device is an older type but there is still an API you can use. It is a bit more complex as it requires sending an xml data. You can do it via shell_command. Below please find examples from my aplituner RX-V1067:
shell_command:
yamaha_pure_direct_on: "curl -X POST 'http://10.144.1.12/YamahaRemoteControl/ctrl' --data-binary '<?xml version=\"1.0\" encoding=\"utf-8\"?><YAMAHA_AV cmd=\"PUT\"><Main_Zone><Sound_Video><Pure_Direct><Mode>On</Mode></Pure_Direct></Sound_Video></Main_Zone></YAMAHA_AV>'"
yamaha_pure_direct_off: "curl -X POST 'http://10.144.1.12/YamahaRemoteControl/ctrl' --data-binary '<?xml version=\"1.0\" encoding=\"utf-8\"?><YAMAHA_AV cmd=\"PUT\"><Main_Zone><Sound_Video><Pure_Direct><Mode>Off</Mode></Pure_Direct></Sound_Video></Main_Zone></YAMAHA_AV>'"
yamaha_party_mode_on: "curl -X POST 'http://10.144.1.12/YamahaRemoteControl/ctrl' --data-binary '<?xml version=\"1.0\" encoding=\"utf-8\"?><YAMAHA_AV cmd=\"PUT\"><System><Party_Mode><Mode>On</Mode></Party_Mode></System></YAMAHA_AV>'"
yamaha_party_mode_off: "curl -X POST 'http://10.144.1.12/YamahaRemoteControl/ctrl' --data-binary '<?xml version=\"1.0\" encoding=\"utf-8\"?><YAMAHA_AV cmd=\"PUT\"><System><Party_Mode><Mode>Off</Mode></Party_Mode></System></YAMAHA_AV>'"
yamaha_enhancer_on: "curl -X POST 'http://10.144.1.12/YamahaRemoteControl/ctrl' --data-binary '<?xml version=\"1.0\" encoding=\"utf-8\"?><YAMAHA_AV cmd=\"PUT\"><Main_Zone><Surround><Program_Sel><Current><Enhancer>On</Enhancer></Current></Program_Sel></Surround></Main_Zone></YAMAHA_AV>'"
yamaha_enhancer_off: "curl -X POST 'http://10.144.1.12/YamahaRemoteControl/ctrl' --data-binary '<?xml version=\"1.0\" encoding=\"utf-8\"?><YAMAHA_AV cmd=\"PUT\"><Main_Zone><Surround><Program_Sel><Current><Enhancer>Off</Enhancer></Current></Program_Sel></Surround></Main_Zone></YAMAHA_AV>'"
Documentation of the API can be found here: