The difference is US dollar notes have a liability which is paid to banks 'federal reserve' and coins do not have liabilities so coins don't cost USA when issue

The difference is US dollar notes have a liability which is paid to banks 'federal reserve' and coins do not have liabilities so coins don't cost USA when issued. Coins are just issued. Notes (paper dollars and electronic) are loaned into existence and USA pays interest to federal reserve for the USA's own money.