I got an endoscope from China. It works with Cheese on my LinuxMint 17.3 system. It appears to be a normal USB camera.
The software for Android needs at least 4.1.2. My old phone (ZTE T790) only had 4.0.4, so I just bought a HUAWEI Y5 with Andoid 5.1.1.

I've installed the app and plugged in the endoscope, no adapter needed. The app starts, and does not complain about the Android version. The endoscope is not seen. I have another USB camera that works with Cheese, but it also is not seen. An OTG adapter is needed with this camera.

When I use the cable supplied with the phone to connect to my PC I can see and read files that are on the phone, so it appears that the connector is OK.

Perhaps my OTG adapter is bad? Is there a setting somewhere for enable/disable OTG?
It would be just my luck that the phone does not support OTG!

I know that without specific details on camera models and apps answers are hard to come by.