This is what I love about the Legend of Zelda games, it's "rupee", which comes from "ruby":

Rupee is likely derived from or a corruption of ruby, a valuable gemstone. As a result, Rupees were frequently misnamed early in the series, such as the name "Rupy" in the original The Legend of Zelda. In the German versions of The Legend of Zelda games, a Rupee is called a Rubin, which is German for ruby. Ironically, Red Rupees resemble rubies.

They're valuable gems of indeterminate size, not necessarily related to rubies or actual gems (could be glass or something), and have no direct comparison to any actual currency (unlike gold) but we can understand some amount of inherent value (better than credits). It's unique to the game, and denominated as a single number.

Some other ideas for units:

• sovereigns - as long as the person in charge is a king
• in-game term related to the region (like Euro is to Europe)
• chips - could be metal, glass, gemstones, etc

Keep it vague so people don't lose immersion by comparing to realm world units, or not have any inherent wealth. That said, "credits" is better than "gold," just a bit cliché.