Cannot connect to RTMP Server

I am using OBS to stream to my custom RTMP server.
I have triple-checked my server URL and stream key.

Here’s what the OBS log gives me -:

12:14:40.865: Unhandled: :
12:14:40.865: NetConnection.Connect.Rejected
12:14:40.871: rtmp server requested close
12:14:40.871: [rtmp stream: ‘simple_stream’] Connection to failed: -3
12:14:40.871: ==== Streaming Stop ================================================