With these two apps, FPV is possible with the Gear VR.
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Play cardboard eliminates the auto startup of the Gear VR (Oculus) and the CAVU puts the display on the phone for the goggles.
The CAVU is free but limited flight time unless you purchase it.
There's all kinds of options on the display to move the images to get it just right.
Although I haven't used it much, it does work on my Samsung Galaxy s7 and Gear VR goggles.
Just a note, It works via WiFi so no OTG cable can be used.
Good luck

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