Adding more than one Push Notification URL in Developer Dashboard.
Developer Dashboard > Web API Settings
There is no way to add multiple endpoint URLs to the same developer account (whether for testing purposes or to associate with separate channels).
As a workaround, some partners have created a second developer account to set up a separate push notification URL there. You could then create test channels in your secondary developer account to align with the newly-added URL.
We've heard this request from several developers and have passed it along as a feature request to our Roku Pay team