Help with addon 3 way wiring

I got a 3 way switch on bottom and top of stairs. The top switch is wired as usual ( neutral, load, line,traveler, ground all in their respective holes, but im puzzled by the downstairs switch. This is how its wired:

I got 3 cables + ground but the addon only has 2 connectors ( neutral and traveler ) and ground. So if i put the white cable into the neutral of the addon and the red in the traveler, the black cable is left hanging not connected to anything.

Someone help? Im confused on why is the neutral wire going into the black screw connector in the regular switch…

Please have a look at this thread as it should help get you going:


I found this video pretty helpful when I did mine.