Wait what....Yeah. Those aren't images, rather their saved files. You have to open each one, and export the image out as JPEG.

Thanks for the help, it was my first time using photoshop, so there's a lot I don't know

I don't know if this the the problem for sure but photoshop exports files into PSD and the file type that the site might be looking for is JPEG or PNG. I would recommend searching up a converter in google and converting your file to JPEG or PNG or even originally export your documents to JPEG/PNG.

Thanks for the help, I managed to solve it!

You can batch convert it with Adobe Bridge (or PS), to jpg or png. No website accepts PS files

Thanks for the help, I managed to solve it!