I come here late after your question is asked, but if someone finds this topic and asks themselves the same question:
I THINK you're right. I'm trying to create an application using Layar, and I wonder how it works, but as you can see in some tutorials, you can find part of the documentation on your website, it seems Layar requires you to use your own a server for hosting its web services.
(here is a link to one of their tutas as an example, there is an example of the code downloaded that he wrote in PHP, and you should place it on your server and point your server’s link to the “publish layer” of the Layar part to use the application with your own webservice.) http://layar.pbworks.com/w/page/44331092/First%2520Layar%2520Tutorial%2520-%2520Create%2520a%2520simple%2520Geolocation%2520layer
Also, to answer the question about the API endpoint here, as defined by the Layar staff:
"• The URL of your point-based web service. NOTE: Only ports 80 (http) and 443 (https) are supported, so URLs with additional port information will not work." or also "The URL of a web service that provides information about points of interest (POIs) in the database."
Described as mandatory use of the service.
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