If you integrate with Follow Up Boss we ask that you register your system. Once registered, you will be provided with a unique system key. Every request to the API should include the registered 'X-System' and 'X-System-Key' headers.
X-System: AwesomeWebsiteBuilder X-System-Key: 560270f7914b5b4a5f4dc1793ebc2796
On first glance system may look similar to the "source" attribute sent along with lead notification events. The difference is that the lead source describes the brand or marketing name a broker uses for a lead source, and system describes the system used.