In appodeal dashboard, for each app you have, there is a video ad settings where you can set the rewarded video settings, such as reward amount, currency name, and a reward callback URL. Really don't know what that means, as I only check if the rewarded video has been shown. Anyway, they have a live chat in their site and you can ask them, they're fast.
BTW, I know my game is new and I still don't have decent number of impressions, but after a week using appodeal my revenue is ridiculous for 400+ impressions day and growing (yesterday I had 461 impressions and 17 clicks, wich gave me the enormous revenue of $0.10!) I'm testing now adbuddiz, wich has better looking ads, and it's lightweight and requires less permissions...