When the RTMP ingest streaming protocol is selected, two ingest (input) endpoints are created for the channel: Primary URL ...

When the RTMP ingest streaming protocol is selected, two ingest (input) endpoints are created for the channel: Primary URL and Secondary URL. 
Primary URL: Specifies the fully qualified URL of channel's primary RTMP ingest endpoint. 
Secondary URL (optional): Specifies the fully qualified URL of channel's secondary RTMP ingest endpoint. 
The reason the secondary URL is created is to improve the durability and fault-tolerance of your ingest stream as well as encoder failover and fault-tolerance.