How to enable Custom ID field
By default the Custom ID custom field will not appear in the issue panel. To add the Custom ID custom field in the issue details panel follow these steps.
Steps to add Custom ID field
Click on the Configure (gear icon) at the bottom of issue details panel.
In the Issue list select issues for which you want to add the field, and then in the Search Field Input search for Custom ID
If you’re in the new UI of the Jira, and didn’t found the Custom ID field in the search input click on the Go to the Fields page.
On the fields page click on the Add Field.
Search for Custom ID and check the checkbox respected to Custom ID block. Then Click Add Field.
Now revert back to the Issue Configuration Page and search for Custom ID.
Drag the field found to the desired location.
Save the changes, this will add the field to the issue details panel.