Worthy Brothers Pipeline accepted a check marked "payment in full" from a contractor but still sued for additional money owed. The Delaware Supreme Court ruled that old common law rules about accord and satisfaction (settling a dispute by accepting partial payment) still apply, even though the UCC has a "reservation of rights" clause. The court sent the case back to trial to determine if all the conditions for accord and satisfaction were actually met. This matters because it affects whether accepting a full-payment check truly ends a dispute or just pauses it.
A "payment in full" check notation may legally settle a dispute under common law, even if you write "under protest" or reserve your rights on the back
Before cashing a full-payment check, verify all elements of accord and satisfaction are present: offer, acceptance, consideration, and intent to settle a genuine dispute