This story about restaurants that only accept electronic payment set me wondering. I know that under legal tender laws a business can set a policy on what forms of payment it will accept, but that only applies if no debt exists prior to the time of payment. I think this creates a problem for restaurants trying to impose a "no cash" policy. Normally you only pay for your meal after you have eaten it, so the debt is incurred when you eat the meal, and the payment happens some minutes later.
Am I right in thinking that that legal tender laws would apply in this situation? If you provide payment in cash, the restaurant cannot then claim you haven't paid your debt.
Note: not a duplicate of this question because it did not consider the delay between incurring the debt and paying it.