Nginx How to redirect sudomain to external url?

Hi! Im migrating a website for a client. The website was on a apache webbhotell. There was a folder with a index file pointing to an external url. How do I do it with centminmod?

If I for example want the url sub.mywebsite.com to redirect to centminmod.com.
( The domain uses cloudflare )

 

The structure is the same as it was on the webbhotell but it doesnt seem to work.

The subdomain is called j4. So there is a folder in the public/ named j4 and inside it there is a index.php file with this redirect but I just get an error when visiting it. Did I do something wrong?

Code:

<?php
header("location:https://100.20.120.50/login");
exit;
?>

I found this way to do it in cloudflare. I dont know which is the correct way or if it matters?

 

Awesome. Thanks! That was exactly what i was looking for.
One upside with it is that cloudflare only has 3 free rules.