Copy Value From Other Field in Post-function does not show the custom field

Summary

Copy Value From Other Field in Post-Functions does not show my custom field

Environment

Jira Cloud

Diagnosis

In workflow transition when we try to add a Post Functions and select Copy Value From Other Field, custom fields don't appear in the drop-down in both the Source Field and Destination Field

Cause

The Field uses "autocomplete" functionality, so by default only the most used Fields are displayed. 

Solution

Write or type the name manually as the Field uses "autocomplete" functionality, so by default only the most used fields are displayed. When you start writing, other options or Custom Fields are displayed too.