I have a PHP script that connects to an api and posts information to their systems, but when its trying to connect it throws a fatal error:
Fatal error: Unca
I just tested the URL in my browser and got a connection error.
Maybe the problem is with their server (or you have the wrong URL)?
Edit:
Looks like ther server is throwing a 500 error - maybe because the data you're posting is invalid.
You could use a packet sniffer and check the exact data you're sending to the server (or use cURL as suggested by @acrosman)