The stake vs eddie is an onsite challenge, you do not need to visit forum or post anything because it is using automatic system. Once you manage to beat the multiplier, you will receive the reward after the challenge ends. The current on going stake vs eddie challenge looks easy to hit because the multiplier to beat is 343x only but if we look deeper on the slot (fishtastic by red tiger), hitting big multiplier needs a huge luck. You may try it with 100-200 spins but dont force yourself to beat the multiplier.
Depends on your preferences, if you like slots challenge there are several different promotions you can find both in the website and in the forum.
https://stake.com/promotions/promotion/conquer-the-casino
https://stake.com/promotions/promotion/stake-versus-eddie
https://stake.com/promotions/promotion/the-level-up
https://stake.com/promotions/promotion/multiplier-race
https://stake.com/promotions/promotion/chaos-collector
Above are the promotions you can find in the site which works automatically, you dont need to opt-in, no need to post anything. Be sure to read the terms and the most important thing is do not spend too much money because the prize may not worth the risk.