Like all Federal Reserve Notes (FRNs, aka "bills" or "cash"), the $2 FRN is "legal tender for all debts, public and private."
However, a lot of people don't know about them. If I owe someone $10, and all I have is five $2 bills, is it legal for him to refuse to accept them because he's sure that $2 bills don't exist and they must be counterfeit? Assume that for some reason, he can't just Google "$2 bill" and see that they're real.
If the requirement for the debt is that the debt be paid in US dollars, absent some other stipulation to the contrary, $2 bills are US dollars and would satisfy the debtors obligation.
It's hard to envision a situation where one would go before a judge or magistrate to enforce one's right to pay a debt with a $2 bill, but I suppose that effort would be successful. A debt that is to be paid in US dollars can be paid in $2 bill increments.
