How to copy the transition date and time to a custom field

Use case:

How to capture the date and time when a transition is executed and copy it to a custom field using the Update Any Issue Field (JSU) post function.

Instructions

Log in as a Jira Admin and go to the workflow that is associated with your project and issue type.
In the workflow, click Edit to switch to Edit mode.
Select the desired transition and then, select the Post Functions tab and click Add post function.
Select the Update Any Issue Field (JSU) post function and click Add.
If there are no pre-conditions, select Ignore precondition under “Precondition must be:”
Select Within same Issue under “Update field on all issues related as”.
If you want the action to be performed as some other user, enter the user ID in “Perform As User:”.
Note: Make sure this user has edit issues permissions on the issue.
Select the target field (custom field type - Date picker or Date/Time picker) in “Issue Field:” and enter the below value in “Field Value:”.
%%CURRENT_DATETIME%%
Click Add.
Publish your workflow.