I am unsure what distinction the linked page is trying to draw between payment for goods/services and debt. The first paragraph seems to unequivocally state that businesses do not need to accept cash (from a Federal law perspective anyway).
There is no federal statute mandating that a private business, a person, or an
organization must accept currency or coins as payment for goods or services.
Private businesses are free to develop their own policies on whether to accept
cash unless there is a state law that says otherwise.