Do you mean Midi channel 17 ?
There is no channel 17 in Midi, Just 1..16.
Reaper internally does provide 16 "Midi Buses" to extend the concept of Midi channels, but as this is just internally to Reaper it is not a "compatibility" issue, and Reaper can't "recognize" a "Midi Bus" in some external source.
see ->
https://forum.cockos.com/showthread....light=loopmidi
-Michael