This article explains a step by step instructions on how to copy the value of the next due date custom field into the due date field by using COT app.
Instructions
The following is the custom field called "next due date"(custom field type is a date) and its value is set to 18/Dev/19.
You need to use the substitution variable to copy the value from the next due date to due date field.
In the post function, you need Set the Due Date field to %original_customfield_10300%. 10300 is nothing but the Id of the custom field "next due date".Follow the below steps to
customer requirement is like if he does the transitions he wants the value of the next due date field to be copied into the due date field. This can be achieved by giving the custom field id of next due date i.e %original_customfield_11602% in the post functions. copy the %original_customfield_11602% into the following location
go to workflow--> edit the transition --> fields --> due date