Per-file limits and total limits
Why five acceptable files can still be rejected as a set.
Portals publish two different ceilings. Each file must be under a cap, and the whole submission must be under another cap. Passing the first does not imply the second.
Example you can type into File size: per file 2,048 KB, total 4,096 KB. A 180 KB JPEG, a 420 KB WebP, and a 900 KB PNG pass on their own. A 2,400 KB PDF fails the per-file rule. Even if you replaced that PDF with a 1,500 KB file, four files of 1,200 KB would each pass and the total would not.
The limit checker also filters extensions. Turn PDF off if the form is photos only. A case that stays under every cap is included as “Load a passing set”, because a tool that only shows failures hides the path you actually want.
File bytes are read locally. The page does not send the stack anywhere.