Its part of the experience as a bounty hunter. In my case, I have not been paid in half of the bounties I joined especially when I was new and joined any campaigns I find. But now im more particular in joining bounties and look deeply to the project and the team running it.
It doesn't pay to join almost every campaign on here, one should be more careful about these bounties. The problem is about receiving the right information. Try to follow few good Bounty Managers that are honest