Additionally as part of the Phoenix 1.4.x → 1.5.0 upgrade you should change that line to:
{Phoenix.PubSub, name: UserDocs.PubSub}
Assuming you’re already on Phoenix 1.5.x (which you probably should be if you want to be using OTP 24) I would take a close look at the upgrade guide to ensure that you’re not missing any of the other steps: phx-1.5-upgrade.md · GitHub
