You really should just lurk and not post comments about stuff you don't know much about. FRN's used to carry this notice (until the mid 1960's):
THIS NOTE IS LEGAL TENDER FOR ALL DEBTS(FRNs before 1933, weren't legal tender, but were redeemable in gold or "lawful money.") So obviously FRNs were not "lawful money" and they still aren't.
PUBLIC AND PRIVATE AND IS REDEEMABLE IN
LAWFUL MONEY AT THE UNITED STATES TREASURY
OR AT ANY FEDERAL RESERVE BANK.
ML/NJ
Take your own advice.