[Closed] Adjusting travel on SIDs

I just got some SID Teams for my Anthem. I'll need to get them switched from 100mm travel to 80mm - get an LBS to do that, anyway.

I had thought that to drop the travel on a (non U-Turn) Rock Shox fork you needed to add a spacer to its internals. I was told when I ordered the forks that they came with whatever is needed to change the travel but there wasn't a spacer in the box. So... am I wrong about this or do I need to make sure I have a spacer before I take the forks in for their travel adjustment?