USD are a “liability” of the FED.

Ok, during the gold standard, a bank would accept gold and issue paper as an IOU. This would be a liability because they have outstanding paper and gold in custody.

A bank has a “loan” to a customer as an “asset” because they gave paper to the customer and are owed paper.

A bank also has a “liability” when a customer deposits paper because it owes an equivalent amount of paper on demand.

But what exactly does the federal reserve “owe” in exchange for the paper fiat “federal reserve note” if one were to give them one?

Answer: this can’t happen, so why are they a “liability” of the FED?