Built same dimensions as nether portal using both stone bricks and deep slate bricks.

going to need more info?

I had this issue as well when i created the portal frame and made the catalyst i activated the portal. made sounds and everything, when i went into the portal it wouldnt do anything, id be standing there waiting to be take to the dimension but nothing happened

if you are on a server, a /reload and a server reboot might fix it. if you are on singleplayer, you need to make a new world... this is a vanilla bug

Just wanted to post a solution I had, since the /reload (once and twice) and restart didn't work for me at all server side. For those wanting to use an existing world that was created before adding the mod:

• Generate a new single player world with the mod already installed
• Locate your level.dat inside that new world save
• Using an NBT editor (I'm using NBTExplorer here) navigate to "Data > WorldGenSettings > dimensions > undergarden:undergarden"
• Copy the entire NBT entry
• Go to your server world's level.dat and paste the missing NBT entry inside the same location where it should be

Doing this and restarting the server was all I needed to do, and this was also how I fixed another datapack based mod (Nullscape) which suffered the same issue of not populating into the forge dimension registry for some reason.
As always, make sure to backup your world before doing this; this at least worked for me and I hope this helps some other people out there!