[Moderator note]
Snow Pea, in GQ the objective is to provide factual answers to questions. If you don’t have actual information to contribute, please refrain from sarcastic or other useless posts of this kind, especially as the first response to a question.
Colibri
General Questions Moderator
I think the objection to “monies” is akin to the insistence in some quarters that “people” really is the plural of “person” & that therefore neither (the noun) “peoples” nor “persons” are words.
Which is to say, elevating one’s ignorance over true facts one does not know.
Fully agree with several posts above about ‘monies’ representing several seperate and discrete sums.
It is quite commonly used for exactly that meaning within the banking and finance community, and I see the term regularly.
Sort of. While I didn’t care for snow Pea’s snark, he (she?) was correct in noting that often ‘monies’ is used where it’s not appropriate: “All moneys received from whatever source should be deposited in the General Fund.” If you can legitimately conmingle them, folks, they’re not ‘monies’ – they’re just plain money – and you’ll come across sounding pretentious if you use ‘monies’ in order to impress.
“Over a thousand people were gathered…” – “persons” would be singularly inappropriate; “people” is being used as an indeterminate collective plural here. But almost nothing else will work in “The Serbian, Bosnian, and Croatian peoples are united by a common language but divided by religious and other cultural traditions.” Or “Occupancy by more than twelve persons is prohibited by law.”
(Not to mention the problems with theology: “The Trinity is defined as three people in one godhead” doesn’t quite make it! 
Dictionary defines monies as follows:
mon·ies n. A plural of money.
mon·ey n., pl. mon·eys or mon·ies. 1. A commodity, such as gold, or an officially issued coin or paper note that is legally established as an exchangeable equivalent of all other commodities, such as goods and services, and is used as a measure of their comparative values on the market. 2. The official currency, coins, and negotiable paper notes issued by a government. 3. Assets and property considered in terms of monetary value; wealth. 4.a. Pecuniary profit or loss: He made money on the sale of his properties. b. One’s salary; pay: It was a terrible job, but the money was good. 5. An amount of cash or credit: raised the money for the new playground. 6. Often moneys or monies. Sums of money, especially of a specified nature: state tax moneys; monies set aside for research and development. 7. A wealthy person, family, or group: to come from old money; to marry into money. --idioms. for (one’s) money. According to one’s opinion, choice, or preference: For my money, it’s not worth the trouble. in the money. 1. Slang. Rich; affluent. 2. Sports & Games. Taking first, second, or third place in a contest on which a bet has been placed, such as a horserace. on the money. Exact; precise. put money on. Sports & Games. To place a bet on. put (one’s) money where (one’s) mouth is. Slang. To live up to one’s words; act according to one’s own advice. [Middle English moneie, from Old French, from Latin mon¶ta, mint, coinage, from Mon¶ta, epithet of Juno, temple of Juno of Rome where money was coined.]
Are you being subtly humorous here, or do your clients actually need to pay each “money” with a separate check or money order? Typically when I’ve rented an apartment, the lease does itemize separately the initial security deposit and rent. But I’ve never been asked to pay them with separate checks.