For the hundreds of repairs I've done and assisted with, 90% of the customer service issues I have are around binding issues for DJI Phantom 2 Vision (base or plus) with the range extender.
Any questions not covered in this page, please feel free to contact me.
It's not a straightforward process and to add to the difficulty, you also have the fact that the binding process actually won't work on some modern cell phones and tablets. For example, my Samsung S7 Edge (Android 9) will not perform binding through the DJI Vision app, but my Samsung S6 (Android 6) and Moto E (Android 6) will both work to bind range extenders no problem! Old iPhones like iPhone 4 are similar are also reported to work for binding successfully.
The key to having successful binding using Android is to use the DJI Vision App (from the Apple or Google Play App Stores or sideload the APK) on an old device with Android 6.0 or earlier.
Whenever you see no telemetry (distance and speed numbers) and an error in the Camera section of the DJI Vision app saying, "Connection Broken," then binding is your problem. However if you see telemetry, but a blank FPV, then it's usually a sign that your module needs repair (or your connections are bad).
Below find a video of a successful range extender binding:
Below, find a video of an unsuccessful range extender binding (caused by newer phone/tablet hardware that is not fully compatible with the binding feature of the DJI Vision app):
If you can't bind with your phone, borrow (or buy) an old android phone to try the procedure on.