How do I find acceptable values in customfield_10006 - Epic link

[anju kohli]

1st question:
How do I find acceptable values in customfield_10006 - Epic link?
What is the format or field value of Epic Link field?

2nd question: 
In the #if ... #else ... #end. The #else section runs successfully but in #if section I get below error:

• com.atlassian.sal.api.net.ResponseException: Error communicating with Jira, {"errorMessages":[],"errors":{"customfield_18608":"Field 'customfield_18608' cannot be set. It is not on the appropriate screen, or unknown.","customfield_18609":"Field 'customfield_18609' cannot be set. It is not on the appropriate screen, or unknown.","customfield_13355":"Field 'customfield_13355' cannot be set. It is not on the appropriate screen, or unknown.","customfield_22701":"Field 'customfield_22701' cannot be set. It is not on the appropriate screen, or unknown.","customfield_18612":"Field 'customfield_18612' cannot be set. It is not on the appropriate screen, or unknown.","customfield_18601":"Field 'customfield_18601' cannot be set. It is not on the appropriate screen, or unknown."}}

[Trudy Claspill]

Are you working with Jira Server/Data Center or Jira Cloud?

The Epic Link field is an Issue Key type of field. It is supposed to contain an issue key (i.e. ABC-123) for an Epic type of issue, which would be the parent Epic for the issue where the Epic Link field exists.

Regarding your second question, is your code trying to set fields while creating an issue or editing an issue? For the former, those custom fields must be added to the Create Issue screen for the issue type(s) you are trying to create. If you are trying to edit issues, then the fields must be added to the View/Edit screens for the issue type(s) you are trying to edit.