Request Permission to Escape - S1-E32
Trivia: When Carter first goes into the bar, the Artillery Private he speaks to is played by William Christopher, who, besides a couple of other spots in the series, is better known as Father Mulcahy at the 4077th Mobile Army Surgical Hospital, or M*A*S*H.
Answer: It's a comedy, not a documentary.
stiiggy
Perhaps it was counterfeit. There are numerous episodes where they deal in counterfeit monies.