How does one select a specific 960 position when challenging somebody?

I'm running a 960 tournament where the players organize their own time to play. Some prefer chess.com, others prefer lichess. On lichess you can select the specific 960 position from a list when challenging somebody, but on chess.com I don't seem to see it anywhere

When trying to copy and past a FEN, an error happens saying that the pieces are in incorrect positions for castling. The castling works just fine when loading the FEN into lichess

What is the reason for this? Is there any way to fix this?

Here's the FEN we use that works on lichess: nnbbrkqr/pppppppp/8/8/8/8/PPPPPPPP/NNBBRKQR w KQkq - 0 1

If you can pick a setup, you can probably develop openings to use.

Seems like the whole point of Chess960 was to eliminate opening preparation.

Okay, I understand that, but these are casual games so such a restriction shouldn't apply. Also, being able to look at the position ahead of time is not only allowed, but encouraged for the tournament. Part of the spirit of the tournament is studying these mystifying positions.

So do you not know of a workaround? It doesn't seem right that the PGN works on lichess and not on here