...
Only user have permission Edit can inputted the values.
On In the issue screenIssue Screen, Jira have two mode ( issue create, issue viewIssue Create, Issue View).
In issue create Issue Create mode, permission Edit is required. The user can input the values in the custom field.
...
In issue view Issue View mode, the user have permission view or edit will see the value of the custom field.
...
Click on this custom field to go Edit mode.
...
if user don’t have permission
...