What can I do with favors?

I got a favor from doing a trade with some AI, but if I click on the favor in the diplomacy screen, it opens the trade window, and at that point, I can see no favor.

Does this mean I can do a trade that is unfairly balanced to me? IF so, how do I know if a trade used my favor or not? or what other use does this favor give me?

Solution 1:

I usually find favors to be worth around 100 flat energy. However, as with all resources, their value fluctuates according to other factors in the game. For example, Samatar Jama Barre (African Union) recently offered me 3 favors for 7 Xenomass. And, as @PhilipPittle mentioned in his comment, you can (sometimes) force AIs into war with you! YES YOU CAN, AND IT'S GLORIOUS!

I'm not sure what the parameters are, but it is possible. Elodie (Franco-Iberia) offered me a favor in exchange for a nominal amount of strategic resources. Fast forward probably 100 turns or so, Hutama declares war out of nowhere. I go to my allies (Elodie being one of them) and first try to bribe them, that doesn't work, then try discussing war. Elodie said no, BUT I had an option that said "I must insist, as payment for the goodwill I showed you earlier (-1 favor)." I obviously chose that option, to which she said, "I will mobilize my troops at once." :D

Remember the 3 favors from the Samatar Jama Barre? I went to him right after Elodie. I had a total of 4 favors with him at that point, but I didn't get the option to force him when discussing war, nor would he take a bribe of all 4 favors.

As I mentioned, I have no idea what the parameters are. I had a cooperation agreement with both Samatar Jama Barre and Elodie, but I had been holding on to Elodie's favor for much longer. Hutama was Purity, Samatar Jama Barre was Harmony, and Elodie was Supremacy.

There are simply too many factors to even guess what caused the option to appear, but the point of my answer remains: It is possible to use favors for more than simple trades.

Solution 2:

On the deal screen, the first item on the 2 lists should be "Gain Favors" and "Spend Favors" (in the Red boxes on the image below). Favors are not spent automatically, you have to put them "on the table" like any other trade item.

Basically you can use favors in trades like a currency to make your deals more enticing. I often find myself trading them back for Energy.

As mentioned in another answer, sometimes when using "discuss" to ask an AI for things (such as declaring War on another player) you will have the option to press them in exchange for favors. However this option seems to only appear if you have enough favors with them to suceed.

I have also read that when you confront an AI about something (such as them spying on you, or settling too close to you) and they say no, you will sometimes have the option to spend favors to make them agree to stop. This also does not happen all the time, only if you have enough favors.