flask_uploads.exceptions.UploadNotAllowed

First, Flask-Uploads is a Flask extension that provides file upload support for Flask applications. The flask_uploads.exceptions.UploadNotAllowed is an exception that is raised when an attempt is made to upload a file that is not allowed according to the configured upload sets. This exception is typically raised when the file extension or type is not permitted for upload. When this exception is raised, it indicates that the upload operation is not allowed due to the file type or extension.