Html gauges for touch screens require texture material name with$

texture |

This is the material ID of the screen where the instrument will be drawn.

IMPORTANT! Previously - in FSX - this string needed to be preceeded with a
$ sign. However in Microsoft Flight Simulator this should not be used as
it is now used to indicate to the engine that the material is a collision
material, which is obviously not the case for gauges.
I believe the Important warning is misleading for html touch screens and a
collision material is required for touch screen gauges.

For touch screens, you can leave the $ out… but you need to set the material
in the 3D to be a collision material…