CI 4 Output Compression

READ:
CodeIgniter 4 User Guide - Encoding

Thanks, i am new on web programming. I have read that but still not sure how to make it works. I've tried this code on controller :

$negotiate = \Config\Services::negotiator();
$type = $negotiate->encoding(['gzip']);

But the output still not on gzip encoding.
I am using ajax call to controller and check the content encoding on firefox with inspect.