You mentioned you don't know much about http protocols, but you must have some information on it, since it looks like you almost have it right.
After you open the connection, you need to send a request line, followed by any header lines you want to send. And that is what those lines you are sending are.
When you do it in a browser, it is doing an http GET, not a POST. You are just trying to trigger your flow, and are not sending any data to it. So you might as well just do a GET in your code. Using a POST instead of GET would not give you that 400 error. But I have seen forum messages where people have tried a POST (without POST data after the headers) - they don't get an error, but the flow doesn't run.
You absolutely need a forward slash at the beginning of your request line, just before v1. That might be causing the error.
You said the quotes are wrong in your message, but ok in your code. Just to be sure, I will mention that the HTTP/1.1 should be at the end of the request line, not on a separate line.
So the request line should start with
GET /v1/events.... and end with ….wsF3 HTTP/1.1
Your host header line is ok.
Be sure your code is sending those lines with a CRLF (probably \r\n in your code) at the end of each one, and one more CRLF at the end (more or less a blank line) which tells the host it’s the end of your headers.
You said you are using http instead of https. I would think that should work, the Maker Thing is meant to be talked to by homemade code and https is way more complex. But if it still doesn’t work, you might contact Stringify to verify it will work with http.