Set Value of custom field B with current value of custom field A with smart value

[Tyga4cash]

Lots of similar posts but none with a specific answer to this simple problem:

Using Automation for Jira add-on

I have 2 custom fields, Customer Name and Cust Name (which is a dropdown)

When Customer Name is changed, populate Cust Name with identical entry

in a new rule, I have

"When value changes for Customer Name"

then 

Edit Issue fields

Cust Name

{{issue.fields.Customer Name.value}}

this does not work at all... I tried about 200 different things including Advanced and every other permutation that can be thought of...nothing.. 

Please advise to what simple thing I am missing.. thanks

[Nic Brough -Adaptavist-]

What add-on are you using to try to do this?

[Tyga4cash]

automation for Jira add-on