Guildheists not available

I am attempting to do the level 50 quest, "Hest of the Best" which requires me to complete the guild heist "hero on the half shell." However, I only have 3 guild heist available to me in duty finder and when I speak to battlewardens. I received an in-game message from the support desk instructing me to create a post in these forums. Thanks.

You have to beat them all to unlock further ones. Hero on the Halfshell is the 4th one on the list.