Underground Claim

[Sinyu]

So i just opened my first minehole and i found a huge personal claim a few tiles(7-10) next to my mine entrance.I digged right into that direction to confirm, that it is a personal claim and not just a bug, because it is really huge i cant find an end.
I tried to stake a personal claim too, but it didnt work.

Can someone explain, what exactly i have to do to get an underground personal claim. I tried to pave/ lay stone didnt work either. Whats the trick? Please describe detailed.

[TeckXKnight]

Please read other topics of similar natures. This was just posted in a near identical topic on the front page of 'How Do I'

Building
It should now be possible to build essentially anything in both caves and mines. A couple of restrictions apply:
Caves: You can only build on paved ground. Tiles cannot be paved if there are (black) nil-tiles or water tiles anywhere within a 5x5 area around the tile you are trying to pave.
Mines: An area 6x6 tiles in size surrounds the mine ladder entrance. No constructions can be built on these tiles.

[Sinyu]

I used search. The other post came up after i asked my question. But i then continued posting in that thread. What was posted there neither helped me nor the other guy asking for help.

[sabinati]

you can build a personal claim on a paved cave tile.