Can't see any files inside my external disk

[tom80H]

Sounds like a permission issue.
You could take a look at the Linux Tips section in the #general:tips-tricks-how-tos category of the forum

Linux Tips

Using other hard drives (Windows or Linux) with PMS This How-To is written to help with Internal and External drives. It also is written to demonstrate how to cope with NTFS and EXT4 formatted drives. By logical extension, any format supported by Linux can be handled using the technique shown here. In all cases, the goal is to give user plex permission to read your media files which Linux doesn’t allow by default due to its strict security model. We will walk through the steps needed …