Oppo A73 - OTG USB Endoscope - Not working - Android 7.1.1 ColorOS3.2

Howdy folks,

I've discovered a need to use an endoscope on my Oppo A73 mobile. I cannot get it to work. Here are some details:

Android Version: 7.1.1
ColorOS Version: 3.2
A73 firmware is up to date
A73 supports OTG (On the Go)
FYI: The endoscopes require an app to be downloaded and installed on the mobile for it to interface with the mobile (but you almost certainly know this already).

I've verified that OTG works - the endoscope's light does come on and off when I enable/disable OTG.
I have tried three different endoscopes and none work on my phone
I have tried about 11 or 12 different apps (including the recommended apps by each of the endoscope manufacturers) and same result, does not work
The endoscopes work perfectly on several of my colleagues phones (Samsung mostly, one or two other brands - can't recall them at the moment) and also works perfectly when connected to my PC.

Ive tried rebooting my mobile - still no go.

My assumption is that USB endoscopes don't work either on my particular phone, or there is an issue with Oppo's ColorOS and the apps I am using. So I am considering buying a new mobile but thought I'd ask here first.

So, does anyone who happens to have an Oppo A73 or, for that matter, any Oppo mobile, tried using an endoscope on it and has got it to work successfully? Perhaps you might be able to advise me on how to get mine to work. If you have a different model Oppo and can use an endoscope successfully, what model are you using?

I like the Oppo brand and would consider getting an Oppo A91 as a replacement for me if that model can be shown to have an endoscope working from it successfully. Any Oppo A91 owners out there like to comment on my issue?  (if necessary I may consider a similar spec'd Samsung mobile to the A91 model).

If any of you folks have some experience on this and would like to offer some advice or perhaps point me in the right direction, or can confirm my assumptions (or not) then this would be very much appreciated.

Thank you and regards,

Asterus.