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you can see the stats in their site:
https://flyp.me/
Since it an instant exchange you won't see it on CMC

What is there minimum investment in buying their token, and how often do they pay their investors

No min investment but from what I read in order to get paid you need about 145 FYP.

FYP token hodlers with less than 145 FYP won't receive this Flyp.me payout due to transaction costs.

The last payment was 0.002042878995 ETH per 1000 FYP tokens. But that was during the bull market...
They pay every 3 months but they plan on going to 1 month once Eth's transaction costs go down.