Hey Tarun,
Thanks for responding! I was trying PNG as I assumed it was the highest quality but didn't try JPG. Clicking SHOW didn't provide anymore information unfortunately so I gave up on Print Inc
I decided to switch to Vista Print to print some A3 posters and A5 flyers and I've had absolutely no issues uploading the image.
I also opened up the PNG in Photoshop and other programs and the resolution and size was exactly as it was on Adobe Express
So I've concluded that this issue must be with P
...