Upgrade cost currency change

(i blabber a lot here skip to bottom for tl;dr)

So for my game (who’s update has been on hiatus for almost a year now) I added a special side layer that I called “Meta” which contains various upgrades concerning the playthrough, but are more for in-game progression rather than a boost. For all of these upgrades I have to use a different currency, but I don’t know how to do that. And yes, I know this question has been posted (so this is sort of a repost), but the guide says:
“currencyDisplayName: optional. The name to display for the currency for the upgrade.
currencyInternalName: optional. The internal name for that currency.
currencyLayer: optional. The internal name of the layer that currency is stored in. If it’s not in a layer (like Points), omit. If it’s not stored directly in a layer, instead use the next feature.”

My question is: why isn’t currencyInternalName: player.p.points work (for example)?