They have to accept cash in any denomination as payment for debts, just not as payment for goods and services.
That's wrong. See the link to the Fed in my last post.
It says: "This statute means that all United States money as identified above is a valid and legal offer of payment for debts when tendered to a creditor. There is, however, no Federal statute mandating that a private business, a person, or an organization must accept currency or coins as payment for goods or services." This agrees exactly with what I said: there is no obligation to accept cash as a payment for goods and services, but there is
an obligation to accept cash for debts. If the issue is that you are thinking the words "offer of payment" means that you can offer it but they don't have to accept it, then I think that you are mistaken in your interpretation: offer of payment is a legal term; if an offer of payment tendered to a person with the authority to discharge a debt is refused, then under the UCC that debt is discharged. If I am billed an amount and offer payment in full in cash, my creditor cannot refuse to accept it.