Error: unexpected server response (200)

I’m trying to connect as a socket client to a socket server with this code:

let socket = new WebSocket('wss://' + serverConfig['host'] + ':' + serverConfig['port'] + '/some/uri', {
    perMessageDeflate: false,
    rejectUnauthorized: false, // Server is self-signed for reasons.
});

In this specific instance, the host is 192.168.0.57 and the port is 443. Unfortunately, it throws this error:

Error: unexpected server response (200)
    at ClientRequest._req.on (/var/www/html/node_modules/ws/lib/WebSocket.js:650:26)
    at emitOne (events.js:96:13)
    at ClientRequest.emit (events.js:188:7)
    at HTTPParser.parserOnIncomingClient [as onIncoming] (_http_client.js:473:21)
    at HTTPParser.parserOnHeadersComplete (_http_common.js:99:23)
    at TLSSocket.socketOnData (_http_client.js:362:20)
    at emitOne (events.js:96:13)
    at TLSSocket.emit (events.js:188:7)
    at readableAddChunk (_stream_readable.js:176:18)
    at TLSSocket.Readable.push (_stream_readable.js:134:10)

This is baffling, since I’m basically being told that it’s an error that the response was OK. I hope there’s something wrong with my request, but the error message is utterly uninformative.