Manacoin (abbreviated as mc) is an ethereal currency that only exists as shared thoughts in the astral plane. Everyone can create astral "wallets" to store manacoins. Wallets have names, which can be used to put money into them, and activation words, which are used to take money from them. A wallet can be tapped by anyone who knows its activation word, so be careful and keep your words secret - but do let people know your wallet's name so they can transfer to it.
To make payments with manacoin, use a cantrip to state you are moving a given amount of money from one of your wallets to someone else's wallet, identifying both the giving and receiving wallets by name. The cantrip will feed this information to an ethereal monster, of a species called "chainblock".
Chainblocks eat all information sent to them. When they have eaten enough they die in an explosion, after which the digested knowledge is accessible to anyone who is capable of accessing the astral plane (a broadbelt link is recommended), and the most recent manacoin transfers are present in that knowledge.
Chainblocks can only eat so much, though, and your cantrip is competing for stomach space with everyone else's, so you my have to wait for a few blasts until you find your transaction. If you are in a hurry you can include more manacoins in your cantrip, to fatten a chainblock beast faster.
Last but not least - manacoins are made of the chainblock beasts' scales. Everyone can have a go at the exploded beasts' scales to coin new manacoins. However, only some people manage to do so whenever a beast explodes.
It seems like chainblocks are evolving into a form which is ever less scaly, so it takes ever more powerful spells to get the same amount of manacoin per dead beast. At some point it won't be possible to mine for new manacoins. This, along with the fact that no empire has been able to completely regulate it, and its high demand in the forbidden markets, has caused the value of manacoin to soar in the last few years.