Once you have setup Domain Forwarding Service for your domain name, you need to modify your Name Servers to the ones specified by N/A. Generally, the Domain Forwarding Service should start working within a span of 24-48 hours post modification of Name Servers.
Additional Information
Do not be confused when you encounter errors such as No NS A records at nameservers while using some DNS Tools like DNSReport.com. This does not indicate an error and will not affect the Domain Forwarding of your domain name.