What iPhones support OTG?

With the limited information that you have provided, It is hard to even guess the problems faced by you. 

You may get faster and better responses to your query by --> Writing an effective Apple Support Commun… - Apple ...

Please re-post with detail so that someone else can help.

If by OTG you mean Over Toaster and Grill then

Please see the complete list here --> iOS - Home Accessories - Apple (IN)

See if this helps --> Using USB accessories with iOS and iPadOS

Here’s the article I found trough the internet…

Link:

https://techshift.net/can-iphone-do-otg/

I’ve not heard or seen “USB On-the-Go” in at least a decade, if not longer.

Is this what you mean?