Oauth2 (Dropbox) on iOS

[Ben Rubinstein]

I feel I've been through this before, but I've not been on it for a while, and 
I'm still (again) stuck.

Using Oauth2 to connect an app to the Dropbox API works fine on desktop.

On iOS, I get the overlay; with the Dropbox log-in; I sign in, and it then 
shows the message that this app would like access to the files in Dropbox, 
with buttons (from Dropbox) Cancel or Allow (and a link "Learn more").

However, neither the Cancel nor Allow buttons do anything. Fortunately there 
is now an LC 'cancel' button at the bottom of the overlay (thanks Monte! 
https://github.com/livecode/livecode/pull/6315).

But something's not happening which should (I assume) happen when the user 
touches "Allow". (There is a tiny bit of visible feedback.)

I know on a previous occasion I solved my issue with inclusions, but I don't 
think that's the problem this time. I have (manual inclusions) the Browser 
widget, the JSON and Oauth2 libraries, and the internet library. The call to 
Oauth2 is wrapped in a try block, and I'm not seeing a catch (can't be sure 
that I would, but when I use the new emergency cancel, my script just reports 
"Not authorised" where if I drop the Oauth2 library, I get a dialog reporting 
the catch).

What am I missing? Is anyone else able to succesfully connect to Dropbox using 
the Oauth2 library on LC 9.0.0, iOS 9.3 (or any similar environments)?

TIA,

Ben