The IssueType value set to the code element is a required binding. There are several issues with the four codes listed under Code (Unavailable, Timeout, Badrequest, Nonfatal). 1) Unavailable, Nonfatal, and Badrequest do not exist in the IssueType value set. 2) the codes are listed with the first letter capitalized, Timeout instead of timeout, as the codes are case sensitive. 3) Also, it is not clear if the guide allows to use these 4 codes only or they are listed as most common errors for Prior Auth use cases. 

Suggest to add hyperlink to OperationOutcome that points to the OperationOutcome resource.