Import .m3u music playlists to PLEX on a Synology NAS

There is a way to import your music playlists to Plex, hosted on a Synology NAS. It requires some technical skills though.
This guide -with a few tweaks- should also apply to other environments if you follow the logic/idea of it.

Step 1: Get some vital library information from Plex

1. First of all, go to your Plex installation directly on your NAS. The url should look something like: http://nas:32400/web/index.html#!/
2. Go to your music library and play a song. Now, in the ‘play’now playing’-bar in the bottom, press the 3 dots and select ‘get info‘
   • You can now see the full path to your music directory and this specific song /volume1/Plex/Library/Music/iTunes Media/Music/(artist/album/)song.mp3. Copy the path to your music root directory and write it down somewhere.
     I’ll call this [ROOT] from now on.
   • Now click “View XML”. In this XML there is one thing you need to find and write down the number X: librarySectionID=”X“ (that X should be a number, e.g. 5)
     I’ll call this [ID] from now on.
   • You can see that the url in your browser has also changed to something quite complex.
     – Save the first part of this url:
     https://212-71-14-205.079b54zed68d656d46zb6d5462989a9ec0.plex.direct:32400/library/metadata/115…
     II’ll call this [HOST] from now on.
     
     – Also at the very end of this URL, you will find your unique and temporary Token: …&Plex-Token=97g4cDJqi4APq8aUmvyh
     II’ll call this [TOKEN] from now on.

Step 2: Prepare your playlists to import them to your Plex library

There are a few prerequisites to allow the proper import:

1. Your playlists must be .m3u files and should preferably be localized in the [ROOT] directory of your Plex music library
2. If you open/edit them with a text editor, it’s content should look something like this:
   EXTINF:520,Prince - Purple Rain
[ROOT]Prince/Unknown Album/Purple Rain.Mp3
EXTINF:230,Aha - Take On me
[ROOT]V.A_/Unknown Album/Take On me.mp3
...

Important! All the directory slashes must be forward slashes in this file(!) because your NAS is a unix system.
TIP: You can always use ‘find and replace’ to change force the [ROOT] directory in front of all tracks. Also,

Step 3: Import .m3u Playlists to plex with Postman

First, carefully prepare/compile the following url:
[HOST]playlists/upload?sectionID=[ID]&path=[ROOT]Playlist.m3u&X-Plex-Token=[TOKEN]

So, as an example, it should end up looking something like:
https://232-49-13-205.089b422c68dzf4z6e5a9ec0.plex.direct:32400/playlists/upload?sectionID=5&path=/volume1/Plex/Library/Music/iTunes Media/Music/playlist.m3u&X-Plex-Token=97g4cDJq7dzJz8aUmvyh

1. Run “Postman” (Download, or run online). You will need to create a free account first.
2. Click ‘New’, select “http”, and Change the ‘GET’ to ‘POST’ in the left panel, paste the url, and click the blue ‘Send’ button.

If all went well, you should see a green “200 OK” text appear below in the ‘response’ box, and your playlist should be added to PLEX!
If it didn’t work, there is a chance [TOKEN] has expired, see if you can start a new song and check if it’s still the right one.

Now, in the “Query Params” area, you can just change ‘playlist.m3u’ to ‘playlist2.m3u’ and press send again… and again… to import all your playlists.

I know it’s tricky but I hope this works for you!
Big thanks to Reddit user u/KarmicCamel who figured it out first for a local Plex installation, and for u/jetrolorko/ for pointing us in the right direction for a remote Plex installation.