I'm trying to upload an image that is a jpg file, but the error says it's not jpg
Can you upload it to the forum for us to take a look?
These uploads seem to be error messages. We need to see the actual file that was rejected.
That message tells us what you said. The system does not accept your file. Just to say: it is not enough to rename the extension to something to get a valid file. It still needs to be a file corresponding to the allowed file formats.
See my message https://community.adobe.com/t5/stock-contributors/won-t-accept-jpg-file/m-p/12216394#M33002 and answer that one.
Same. Did you look at your file in the forum. What do YOU see?
Well, if the system says you it's not a JPEG file, then it's not a JPEG file. Please open the file with a text editor like notepad or notepad++, and report the first four characters.