Hello, I’ve tried record digital piano Yamaha P-125 stereo sound. Only left side played. Could you help please?
I can hear stereo in headphones and I’ve tried both headphone port and L+R port.
Interface m-track duo
Update: Problem solved
Close the question please
For the benefit of anyone else with the same problem - what fixed it? Different leads?
I’ve tried two mono cables and worked. But I still don’t understand why single stereo cable does not work, especially in the headphones jack 
The TRS connection (output) on the keyboard is stereo. The TRS connections (inputs) on the interface are balanced “mono” so you have to connect both inputs. Usually channel-1 is left and channel-2 is right.
From your picture, it looks as though you are using two 1/8" to 1/4" adapters. I have had unreliable connections with these adapters in the past. You may find that a single 1/4" cable end-to-end will prove much more reliable.