JMWE shows an error message on the issue view if any error occurs during the execution of the post-function. This message is displayed only if the current user is a Jira administrator.
When you add this post-function to a transition and trigger the transition, the add-on copies the value of the specified user property for the current user to the selected destination field. The user property is used to store extra information about a user. These properties come from the User properties editor page in the Add-ons section. These properties are different from the User Properties you can edit from the User Management section. To add/edit user properties of a user, see the Add/edit/delete user entity properties in User property editor page.
Create missing value(s): Allows creating any missing Component/s or Version/s while setting or copying a field that expects Versions or Components. Note this is applicable for version and component fields.
When setting the Issue Security field, the user property must contain the name of the Security Level, which you can find by looking at the links associated with the Add/Default/Delete operations on the desired Security Level (on the Edit Issue Security Levels screen).