Other Relationship - Pulling in Sales Rep to Billing/Bill Payment

My team has requested to have sales rep notified when a bill payment goes out in specific scenarios.

I set up the workflow to shoot out the email no problem, but the thing I am struggling with is getting the sales rep email. It is struggling to traverse from bill payment > vendor relationship, use the other relationships functionality > customer record > sales rep > sales rep email.

Has anyone else been able to traverse from the vendor record to the customer record via the other relationships?

Workflow parameters attached. These current settings produce an error stating "One

or more recipient emails are not valid." because it cannot traverse that many records. If I switch it to go to a specific individual then I do not have this issue. It does not appear that I can bring the other relationships or sales rep fields into the bill/bill payment.