autoCompleteUrl in editmeta of some fields


I’m trying to use editmeta fields to determine how to render the data for editing of certain fields. For example, if the field is type user, it has an autoCompleteUrl that’s actually a link to /rest/api/3/user/assignable/search endpoint. However, for some of the custom fields that should be editable, I get forbidden (403) when trying to access those url’s.

For Approvers field which is a multiuser picker field, in the editmeta I get that it’s editable (have add, set or remove items operations available so I guess it’s editable) but the autoCompleteUrl is /rest/api/1.0/users/picker?fieldName=customfield_10003&showAvatar=true&query=. Why is there a difference in the API version it’s using? Should I be able to edit this issue (on a sidenote, I’m logged in as the administrator and can update the field in the UI)? Should I be allowed to hit this url with AP.request? Also, could I use the normal rest/api/3/user... endpoint to get approvers for a task?

Same thing with labels. I know there’s an endpoint for labels, and I’m going to use that but I’m wondering why its autoCompleteUrl is also pointing to an older API version? Currently it’s rest/api/1.0/labels/<issueId>/suggest?query=.

Also, while I’m on the subject of fields, could I expect Jira and ServiceDesk custom fields to have constant custom field id throughout instances? For example, “Epic status” field is customfield_10011 on my instance. Is it consistent?