chvetsov wrote: »
Photon Server is server side. Photon Unity Networking is client side.
Server docs: https://doc.photonengine.com/en-us/server/current/getting-started/photon-server-intro
PUN docs: https://doc.photonengine.com/en-us/pun/current/getting-started/pun-intro
Server side is definitely more complex. We recommend to use plugins if you need your own backend.https://doc.photonengine.com/en-us/server/current/plugins/manual
You of course may write your own server side application, but by default, PUN will not able to work with it.