Right, what I forgot in coding to allow ACTION_SEND_MULTIPLE in #Mastalab was that Android 6 doesn't automatically grant permissions, the user has to allow an app the permissions.
Consequently as I forgot to grant read access to external storage for the app it couldn't upload the images.
Fixed now, plus I've coded a simple request for the permission in my version of Mastalab. So my code worked, but my end user was an idiot.
I'm an idiot (;*
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