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If you wish to set a value that it dynamic (changes depending on other variables), see Set a dynamic custom field value for more information.
When are custom field values applied?
Certain configurations will require Custom Fields to be associated with the correct configuration screens. Please refer to https://support.atlassian.com/jira-cloud-administration/docs/manage-issue-screens/ for further information on configuring custom fields in your Issue screens.
Issue Create
JEMHC will attempt to set Custom Field values during Issue create if the custom field is visible on the Issue Create Screen for the associated Project.
Issue update
If a field does not match the above criteria, JEMHC will attempt to update the Issue after the create request has been made. This requires the custom field to be visible on the View/Edit Screen for the associated Project.
What happens if I attempt to set a custom field value to a field not present on create or edit screens?
If the field is not set in the create screen, it attempts to be updated using the edit screen. If the field is not visible on edit, you will receive the following error in the audit report (where X is the field without create/edit association):
Field 'X' cannot be set. It is not on the appropriate screen, or unknown
To resolve this, the field must be added to either the issue create screen or edit screen.