PUID/PGID are used to map the internal docker user with a user on your NAS. This is a simple guide on how to obtain them
First of all we need to activate SSH on your NAS. This is done in the control panel. Its a good idea to disable this after you have obtained them.
There are many apps to ssh onto your NAS (such as PuTTY but I just use the bash client that now comes with Windows 10.
Open bash and use the command ssh firstname.lastname@example.org replacing with your user and IP address of your NAS. Now use ‘id admin’ or whichever user to wish the get the UID and GID for. This will then give you the code for each (1024 and 101 in my case)
Remember to turn off SSH on your NAS when you’re done