File Type Not Permitted when Uploading Media
If you are uploading files in the media library or within form elements on your WordPress site and receive this error:
Sorry, this file type is not permitted for security reasons.
The way to resolve this it to edit the wp-config.php file and copy/paste the below code snippet above the /* That’s all, stop editing! */ line:
Another option is the WP Extra File Types plugin, which allows you to control which file types can be uploaded.