Hello,
I have a ship ive been working on for a side scroller mobile game. To get my ship to move using a physics thruster and impulse, I used the axis mapping reference to “get boost” which returns information from input axis “boost”. This is tied to the space bar in the axis mappings. I would like to have this same set up work with a UMG Widget button, but I am unable to use a UMG button in the axis mappings. I am curious if there is a work around for the UMG buttons to work with axis mappings or what ever. This is my set-up I believe I would have to rework it to somehow include the UMG button so the game would work on mobile. I’m not sure how I would rework it to make it work, I havnt ran into this problem before. The problem is that “Get Boost” function because its tied to the space bar. Everything else will fire with the UMG button, but not that. Any help is greatly appreciated! 
UPDATE: I removed the “get boost” function and replaced the value with a 1 and this seems to have resolved this issue. I have not tried to make my set up work on a mobile yet just in PIE.