Business Rule to Email Assigned To of Master Customer

Hello, I am trying to create a business rule to send an email targeting the “assigned to” of our parent customers when a new opportunity is created in a child account. I created the following rule to send the email notification and received an error message when validating it. Is there a different way to build this rule in order to send the email?

The Rule:
User Who is assigned to the Customer related to Customer related to Opportunity

 

The error message I got is: Data does not currently exist in the system: Module relationship

 Thank you for your help