In many traditions, the feywild's nourisment, what keeps it going, is emotions, memories and stuff like that.
Oh, and most promises made are made with the force of gaes, even casual comments, so long as they are sealed with consideration (which can include food, drink, a token, etc).
Nothing in the feywild is ever given for free. Someone who wants to give something for free arranges a bet that they then lose. Now, faking that kind of a bet then winning it is fair game.
Everyone in the feywild is plotting. The more convoluted the plot, the better. Winning by doing a simple plot is no victory at all.
Karma is a real thing in the feywild; harm someone and the harm does reflect 100 fold. This is one of the reasons behind said convoluted plots; you literally are trying to fake out karma itself.
If you kill someone, you are karma's bitch. If you get someone to agree to be killed by you 'freely', you are far lighter off. If you get someone to agree to make a bet with a 3rd party then stay in a city for a year and a day, who then pays off a debt, which frees another fey from an obligation, who made a promise to then carry a bucket of water to the center of a desert, which fullfills a bet between two other fey, which results in one of them having promised to burn down a city... that is going to insulate you from the consequences for at least a few centuries.
Arranging that kind of convoluted scheme requires grease, and favors are the grease that runs that kind of thing. Your archfey finds arrangements for other fey who want to do favors by tracking down down-on-their-luck fey and making them offers they might not refuse. The fey who want to do favors aren't ones to actually do this for a favor (they are too wealthy to want to owe the archfey anything), so those customers arrange for memorable events for the archfey to capture.
The players actions are (a) built around making memories (with they archfey is harvesting), (b) trying to sow some chaos, to make some down-on-their-luck fey for the archfey to sell "favor access" to, (c) disrupting a rival supply of emotions, which the fey beasts where going to be used to harvest.
The seeliee court mainly deals in love, joy, humour, warmth. The unseliee court in pain, hate, angst and cold. You'd think that would make one good but not the other; but remember, they take away those emotions and use them as nourishment. Which would you rather sell? The best day or your life, or your worst?
Which is another possible job for an underworld fey -- brokering emotions and memories between the courts. When a seeliee court member gets pain, or an unseeliee gets pleasure, someone has to arrange a swap before they each get sick.