Thanks, i was looking for something like this.
Couldn't find error messages to do with prayer but kris helped me out.
I'll post here incase this is ever updated.
In the event that you're trying to setup quick prayers while in combat:Code:You need a Prayer level of (Requirement) to use (Prayer_Name).
If you haven't unlocked rigour / augury yet:Code:You can't set up your prayers at the moment.
Code:You have not unlocked that prayer.Spoiler for source: