You can ask for money on Twitch, as long as you comply with the "Acceptable use of bits" policy, like
@actually said. And as far as I'm aware of, it's perfectly fine to have a "fundraiser" if you're careful with what you say, (even if it's a personal fundraiser).
Now in Twitch's TOS there is a section that prohibits to make 'solicitation offers', however I believe this is only applied when done through spam/junk mail, as you can see in the image, (charity requests is included, if it's done through those means), e.g. having a bot to send offers through PMs to new visitors.
There is another thing that makes me sure of this, and it's that it includes "contests" & "charity" on it. You can do those on Twitch, (charity has been done, and DSP's Minecraft contest was acceptable to some Twitch Admin), so this section must only apply when done through spam.
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