How to make my 3D VR project run on an older Android?

I created a simple maze project that compiles and runs on Unity. and the goal is to run the app on my LG MS870 I think its running 4.0 (its a few years old)

I had followed instructions to install the SDK and selected build versions all the way back to 4.00 and it took a LONG time to download and install all of them.

now I set the phone to Developer mode, connect by USB and do the Build & Run and it compiles and take a couple minutes and says uploading to LG MS870... complete. it starts in developer mode sometimes and has a blank screen, then black Unity screen, then its back on the menu like nothing happened. gone.

I had this happen on my new phone, its an A571VL made by TCL communication ltd, cant remember the other brand name it shows, got this for $10 at the grocery store, small screen. The LG has a larger screen.

Am new to Unity, want to develop for these VR applications but what settings might be preventing the phone from running the app? thanks