Am I missing something?

I thought that was against the law?
Depends. I had this argument before with the powers that be here. It turns out that we were both right. Again, it depends.

Just because backs sell money doesn’t make it ok for you to do so.

Old Currency is exempt from that. And example, old collectible coins, out of date notes, Confederate money, etc.
Nope its not against the law, no different than selling silver coins.
Antique and out of circulation and coins and dollar bills a.k.a. bank notes are different.
Banks sell you money all the time.
That’s called a loan!