This one needs discussion, and I'd rather avoid telecon time on it if possible, so let's please discuss it here:

There are three problems.

• The structural problem is that the error_details structure is always optional, but that's where ticket lives. This could be fixed by moving ticket just outside of error_details.
  
• The spec text problem is that it's underspecified when ticket is supposed to appear. It MUST appear when the AS responds with need_info, and it MUST NOT appear otherwise.
• The example problem is that we've got a need_info example that doesn't show a ticket in it. That's easily fixed once we're certain how to fix the other two.