Help! i completed a task, but i didnt get gems so i asked Fyber Team about it and they said that i need screenshot for proof, but theres no option to send screenshot.

Hi and welcome to forum :)
Check this topic
https://forums.socialpointgames.com/topic/1899/offer-wall-task-i-completed-a-offer-wall-task-but-did-not-receive-any-gems