(a) Tender of delivery is a condition to the buyer's duty to accept the goods and, unless otherwise agreed, to the buyer's duty to pay for them. Tender entitles the seller to acceptance of the goods and to payment according to the contract.
(b) If payment is due and demanded on the delivery to the buyer of goods or documents of title, the buyer's right as against the seller to retain or dispose of them is conditional upon the buyer's making the payment due.