Code for a spell is present in the game but it can never appear in-game. Rather than providing benefits like most spells, this uses the spell system to cause a periodic cost that prevents a negative effect.
Its description is: "Pay your upkeep to the Mercenaries. Should you fail to do this once every hour, your supplies will be cut and your production will suffer greatly. This cost is paid automatically whenever possible, even if you are offline."
The spell has its own autocasting system that attempts to cast it whenever it's inactive. The requisite gold price is enforced by the spell setting its cost to 1 M mana unless there's enough gold to pay the price, in which case the mana cost is 0. If Pay Upkeep were visible but not active, coins per second and click reward would be reduced to 1 and faction coin chance would be reduced to 0%. The gold required is 0 for the first hour and 50 Ocd (5E58) for the second hour. Formula: where x is the number of times upkeep has been paid before.