Visible crew/equipment: As Burkhalter is talking to Strauss and Klink in front of the office door, you can see the shadow of the boom mic moving over each as they talk.
Other mistake: The men are usually all wearing boots. When Carter goes up the ladder, it's clear that he has high-top sneakers on.
Continuity mistake: The whole operation is supposed to be at night, but when the original seven approach the gate to surrender, it's late afternoon, and very light.
Continuity mistake: In the tunnel, Hogan lays out the plan. The arms of the man next to him goes from crossed to by his side between angles.
Answer: It's a comedy, not a documentary.
stiiggy
Perhaps it was counterfeit. There are numerous episodes where they deal in counterfeit monies.