Copy table grid custom field value from Parent to Sub-task

[Yogesh Mude]

Team, 

We have table grid custom field in which users add the field value while creating task. The same field value need to copy from Task issue to sub-task using the post function.

I tried to add copy values from field to field post function from JMWE add-on but its not copying.

Can anybody did this earlier. Any help will be appriciated.

Thank you.