Which reward are you trying to get? I just started trying out the app recently so I have no idea. Maybe try using the website on your mobile browser for now? I've heard the app can be a bit buggy for some things.
in 3 steps
Choose the game that interests you and play itfor free.
Every game has some quests for which you will receive Soul Gems.
You can exchange your Soul Gems for Steam Wallet top-ups, game keys, CS:GO Skins and other rewards.
You know that on Gamehag you can get real rewards for free, right? Join us, complete walkthrough and get your chest!
I wanna know if I am the only one who cannot get the reward via app on mobile as I did many of them but when I use the button "get" there is just a blank page... still waiting for tech team to answer the ticket.