hard cash – das Hartgeld:
hard cash refers to coins and bank-notes(BE)/bills(AE), so this entry is incorrect. Delete.
hard cash – das Münzgeld:
Neither DWDS nor Wahrig have an entry for Münzgeld, but assuming it refers only to money in coin form, this entry is incorrect. Delete.
hard cash – bare Münze:
I'm not sure about this one. Looking around the Internet, I can see (almost figurative) uses of "in barer Münze" where "hard cash" might just work, e.g. in
"In Freiberg zahlt sich die Abfallvermeidung noch deutlicher in barer Münze aus",
but I think there are better translations instead, along the lines of "pay off" or "show real cost benefits". I haven't had time to look into this in detail, however, so I'm not opposing it outright.
demand for hard cash [bank] – der Bedarf an Münzen:
With only 18 Google hits for "demand for hard cash" and only 49 G-hits for "Bedarf an Münzen", where the former is clearly talking about real, liquid money and the latter about the need to mint new coins, this entry is both incorrect and fairly pointless as far as I can see. Delete.
@AE–speakers, does "hard cash" need to be marked "BE" as the OALD entry suggests? I can't find it in Bartleby or Merriam-Webster, but on the other hand there are US websites such as the New York Times that use "hard cash", so I'm not sure.