Unfortunately, GOG added their own layering of netcode and changed the master-server address, making SWBF2SM and therefore SWBF2RM no longer compatible with the game. The only remaining way to host a dedicated server left is to use a multitude of tools and programs to essentially nigger-rig things together. And if that wasn't enough the setup process is also fairly complicated for the average user but if you insist I recommend contacting either LeKeks or Legitosity for support.
LeKeks Discord: LeKeks#6550
Legitosity Discord: Legitosity#1317