A host name leads to a machine; the port leads to a service on it. Proxy services listen for HTTP on one port and for SOCKS5 on another. Mixing them up, for example sending HTTP to the SOCKS5 port, ends in a timeout or a strange error.
On PiratProxies each kind of proxy has its own host and its own pair of ports. For residential they are 8080 for HTTP and 1080 for SOCKS5. The full table is in the docs.
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