I would say that the most likely reason that your notification is not working is because you have probably set the notification "Method" value to "E-mail" and it would need to be set to "Workflow", if you were attempting to use an SRM request notification. Note that this will likely still not work out for you because re-using the SRM request notification for a Service Broker (DWP Advanced) approval will not work. The SRM notification message will contain various keywords, which are surrounded by the "#" symbol, and those keywords will only be replaced if the NTE:SYS-NT Process Control entry has the form name set to "SRM:Request". In addition, the appropriate fields would need to be populated with values that should be replacing those keywords.
I would suggest that you instead continue to use the "E-mail" method, and instead generate your own message text, which can use some of the Service Broker request fields, much like what you see in the "SB Manager Approval New Approval" notification for the "SB Request Manager Approval" process notification.