This is coming in late - you've likely resolved this by now & may be using it for some time. But just in case, I found a discussion thread in the RPi forum where some additional details on the OTG support provided in RPi4 were provided. They may be useful, so I'm posting them here.

This is coming in late - you've likely resolved this by now & may be using it for some time. But just in case, I found a discussion thread in the RPi forum where some additional details on the OTG support provided in RPi4 were provided. Also, this "how-to guide" may be useful in getting this feature working on your RPi 4. These may be useful, so I'm posting them here.