Can't select specific field to copy when two fields have the same name.

Overview:

In some scenarios, if you have custom fields with the same name, then you have to use the ID of the custom field in the post function.

Instructions

Follow the below steps to update the post function with the custom field ID. 

1. Log in to JIRA system as a Jira Administrator and Click on Cogwheel → Issues → Fields (under Custom fields). 
2. Navigate to the desired custom field and click on the cogwheel → Configure.

3. 

4. You will be able to see the custom field ID in the address bar as shown in the following screen.
5. Take a note of the custom field ID's and navigate to the Workflow associated with the project.
6. Edit the respective Workflow and click on the Transition which has the post function with the custom field values.
7. Click on the Post functions tab and click on the pencil icon.
8. In the Create on Transition for JIRA – Create issue(s), click on Custom Fields in the left sidebar. 
9. Now, start typing the custom field ID and select the custom field name in the "Copy original issue custom fields" field.
10. Once you select both the custom field names, it will look something like as shown below.
11. 
12. Click on Update and Publish the Workflow.
13. Re-run the scenario and you will see that the custom fields with the same name are copied to the newly created issues.