How do I properly use curl --post to send data in a request? or What's the correct syntax for curl --

Your JSON might be the issue. Escape those quotes or use a file:
`curl -X POST -H "Content-Type: application/json" -d @data.json http://example.com`

And yeah, curl --post (well, POST) is for sending data—APIs, forms, whatever.

For debugging, try Postman first to isolate if it’s curl or your server.