Legal tender is often misconstrued as an argument. Legal tender laws relate to the settlement of enforcement in courts. Nothing else.
You can require that your customer pays you in Highland Sheep if you want - and refuse to sell anything to them unless they produce those Sheep.
However if you advance them credit (aka creating your own money) and the customer refuses to pay in the Highland sheep denomination as they promised, and then you go to court to enforce your contract, the court can dismiss the case if the customer has offered "legal tender" to discharge the debt.
What legal tender laws do, in effect, is force you to peg your own currency and your own credit advances to the denomination of the state you choose to enforce your contracts in.
Bear in mind you can change the jurisdiction by adding a jurisdiction clause to your contract. Even though I'm in the UK I can guarantee payment in US dollars simply by making my contract subject to the laws of California (say).