Codec not being supported

Hi,

This is going to be quite a long one, I apologise.

I've been an editor for about 4 years now, and never come across a problem quite like this. I was exporting a clients video for spotify, so it needed to be vertical. I was using the 900 x 1600 aspect ratio, which I have used many times for instagram, etc...

I am exporting using H.264, with a custom preset and rendering with maximum render quality.

However, I have tried many ways of sending it to my iPhone, all of which wouldn't let me download it.

I then tried exporting using Apple Prores, HEVC, aswell as MPEG-4, all of which didn't work.

I then took the videos to my Mac, doing all the same things, which also didn't work. I then tried emailing it to a friend, who's android told him that the codec wasn't supported??!! which is weird... That's two computers, three devices, that have all done the same thing. It may be worth mentioning that these videos, when brought back into premiere, work and play as they should. 

My next check, was exporting using media encoder, that hasn't worked either...

As far as i'm aware, no settings have changed since I last exported anything.

Anybody got any tips?

Thanks,

Charlie