Epic Summary = "Part Number"
Child 1 Summary = "Part Number - Start"
Child 2 Summary = "Part Number - Do Stuff"
Child 3 Summary = "Part Number - End"
Trying to get an automation to change part of the child Summary when the Epic Summary changes. For example:
Change the Epic Summary from "Part Number" to "12345-678" would produce:
Epic Summary = "12345-678"
Child 1 Summary = "12345-678 - Start"
Child 2 Summary = "12345-678 - Do Stuff"
Child 3 Summary = "12345-678 - End"
Here is the Automation and error

I've tried multiple combinations of smart values but I must be missing something simple.
Thanks in advance!