We are on the home stretch on getting everything operational. Last issue I have run into is this:
I have an iPhone 7 Plus (iOS is up-to-date)
I have the DJI GO 4 installed (operates on WiFi OK)
1. I turn off WiFi and Blutooth
2. I start the RC
3. I start the DJI GO 4
4. I connect the OTG cable
For a couple of seconds the phone indicates it IS charging from the RC
Then the message "This accessory may not be supported" and the charging indication stops.
I dismiss the dialog box. No connection to the RC is established.
I have tried re-connecting multiple times. No improvement.Note: With or without the Spark makes no difference.
Any ideas?

Thanks, Kingram! The Airplane  mode seemed to be the key.

Kingram Posted at 2018-7-9 13:12
https://www.youtube.com/watch?v=Z2NzGQmHCWU

Good info   

Hi, unfortunately, the usage of OTG cable with the IOS is not yet optimized, I would recommend using a wi-fi connection between your RC and phone. Thank you for understanding.

DJI Tony Posted at 2018-7-10 11:08
Hi, unfortunately, the usage of OTG cable with the IOS is not yet optimized, I would recommend using a wi-fi connection between your RC and phone. Thank you for understanding.

Fortunately when I enter the Airplane Mode it works just fine.

Chuck101 Posted at 2018-7-10 11:15
Fortunately when I enter the Airplane Mode it works just fine.

That's great to know, we would just like to inform you in regards to this scenario what would be recommended.

Chuck101 Posted at 2018-7-10 11:15
Fortunately when I enter the Airplane Mode it works just fine.

Chuck,

You need to cache maps before you fly if you are flying in Airplane mode. DJI GO needs either live data connection during flight so it can download appropriate map or you need to plan in advance of your flight and cache the map of your flight area while you have access to Internet.

Mirek

Mirek6 Posted at 2018-7-10 12:16
Chuck,

You need to cache maps before you fly if you are flying in Airplane mode. DJI GO needs either live data connection during flight so it can download appropriate map or you need to plan in advance of your flight and cache the map of your flight area while you have access to Internet.

Caching the maps is exactly what was done.