Reply To: Sorry, this file extension is not permitted for security reasons.
Yes, the file does first hit your server. However,
.mp4 files aren’t ones that WPEngine forbids, at least to the best of my knowledge. SyncS3 itself doesn’t care what file type you upload. Those considerations are handled at the server and/or Gravity Forms and WordPress levels. That said, MP4 files are definitely supported by WordPress.
Do you have any kind of security plugin that might restrict file uploads? If not, add the following line of code to your
wp-config.php file, and try again:
define( 'ALLOW_UNFILTERED_UPLOADS', true );