On OJS3, we cannot upload the cover image for a new issue. Here's our journal manager:
"I seem to have run into an issue where the cover image for an issue fails to upload properly. Here are a few screenshots of what happened. In short, I was able to drag and drop the .png file of the cover, and it seems to upload, but then when I click “Save” I get an error message saying that only .png .jpg or .gif files are supported (which does not make sense since I uploaded a .png file). I have tried this repeatedly with a .png and also a .jpg and get the same error message each time. Do you have an idea of what might be causing this issue?"