Check in the settlement details if your city is losing money due to corruption. If it is, then you'll need to build a temple that gives you a law bonus (for KH I believe it's the Temple of Zeus). The law bonus (which can be from any law-bonus-giving building) will cut a portion of that corruption and the city will in turn have more income than it would from having a temple of Apollo. Temple of Apollo gives a small tradeable goods increase, which will not add much to your income. Only build the Temple of Apollo in cities that don't have ANY corruption (which are usually cities the closest to your capital or the cities that have tons of law-giving buildings/generals.) Temple of Zeus brings in MUCH more money than a Temple of Apollo.
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