Check the Yammy manual again, you most likely need to configure the output to trigger properly.
If you are certain that the 12V output is triggering properly, then the next step is get your voltage meter and when it should be outputting 12V, see if it is really outputting 12V.
Very important!!! What type of cable are you using? Are you using a mono cable (called a TS cable)? Or a stereo cable (called a TRS cable)? Obviously, we can see this is a 3.5mm output, and you most likely need the TS cable.