As a moderator of a Twitch Streamer, can you participate in a forecast and if so how?
No, you can't. The moderators of a channel are excluded from the predictions.
What should theoretically work is that the streamer withdraws the mod status from you, you then participate, and the streamer then gives you the mod status again. But then you don't take part as a moderator, but as a normal user.
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See also: https://help.twitch.tv/...age=de#faq
Q. Can mods make predictions?
A. No, mods can't participate in predictions on channels they moderate. Mods can make predictions.