me and my fried were making custom challenges today and they were for campaign kills we completed a campaign mission and both of us got at least 50 kills and we refreshed the page and it still said we had 0 kills out of 150 still.
It takes a while to update, it takes a while to process. Basically, it takes a while to do the whole process. You’ll get your credits eventually whether you realise it or not, don’t worry. 
As mentioned above it may take some time for the score to update, but not normally more than 5 minutes after you finish the game/mission. Note that you must go back to the lobby for any kills etc to register.
Did you change any challenge settings? Like, a specific map, difficulty or certain skulls? If the challenge you created doesn’t match what you played, you won’t get the kills etc.
Custom Challenges - The Guide
Part 1: A summary of how to create/submit challenges
Part 2: Specific Challenge Type details
Part 3: Constraints
Part 4: Miscellaneous notes and FAQ
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