You know what sucks more? Having completed all those missions for free and having received none of those prices. I deposited on GG last month for the first time, but I couldn't find that challenge anywhere on my client. Probably because I created my account last December, so it wasn't "brand new".
As for the last challenge, it is indeed not that easy to complete, but you should hit a straight flush (win the Jackpot) every ~15k hands, depending on often you play the suited connectors.
Brutal story: once I saw a player flop a straight flush, only to get counterfeited on the river by a higher straight flush which included only one of his cards (you must use both cards to win the Jackpot)
Back on the topic, completing 25 missions and winning the $T110 should be relatively easy and that's what you should aim for. If you try to hit the Jackpot for an extra $40, trust me you'll pay multiple times that in rake by the time you hit it.
"That's impossible [to hit the Jackpot]" - It is in fact quite probable if you play ~20k-40k hands, only that you'll be paying $650-$1300 in fees while doing that (at $2 Buyin, $0.01 rake, $0.01 Jackpot fee, $0.0125 Bingo fee, every hand for each player, so each player pays $0.0325 in fees every hand)
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