I have small app in flask was is hosted on pythonanywhere. When I try uploading a file I get 500 error. I copied the code exactly except for changing the UPLOAD_FOLDER path and ALLOWED_EXTENSIONS. Local(on my computer) all working good but on server not.
Looks like the problem is in UPLOAD_FOLDER
path value.
Your python script complains it can't find the directory you set up for uploads. And since you set up it as:
UPLOAD_FOLDER = 'upload/'
And in docs this variable has absolute path to the directory, I think, if you change upload/
to
UPLOAD_FOLDER = '/absolute/path/to/your/upload/directory/'
it would help.