WD Photos & iphone 7 - photos on phone not showing in app

I have been using a iPhone 6 plus and wd photos for a long while with no issues. I have just upgraded to the iPhone 7 with ios 11 and after setting up the phone my wd photos app no longer shows any photos that are on the phone.
If I click the folder to upload a photo all I get is a blank screen with a small “c…” at the bottom, if I click on the “c…” it just goes back to empty screen.
I had a read and followed the advice to change the camera format to most compatible but still get the same issue.
Is there any way to get this working or do I need to find a new app.
any help appreciated.

Photos must be saved as jpg on most non-Apple devices. The info from Apple below explains all. Follow carefully. Works for me.