"This file is too big for this device's memory"

Okaysize has no file size limit. But browsers limit how much memory a single tab can use, and phones, especially iPhones, are much stricter than computers. Very large images and long, high resolution videos need the most.

What to try

Close other tabs and apps, then try again. Try on a computer, which has much more memory available. For video, trim the part you need first, or pick a lower resolution in Advanced.