Add Gzip to Plesk Server

Instructions
Login to your Plesk server.
Select the domain you wish to enable gzip for from the left hand side.
Click in Apache and nginx settings:

Down the bottom, add the following to the “Additional nginx directives” field:

gzip on;
gzip_disable "MSIE [1-6]\.(?!.*SV1)";
gzip_proxied any;
gzip_types text/plain text/css application/x-javascript application/javascript text/xml application/xml application/xml+rss text/javascript image/x-icon image/bmp image/svg+xml;
gzip_vary on;

Click OK to save.
Verify with GTMetrix.com

Another way is to set up deflate.

First you need to check the module mod_deflate is enabled on the server.

In plesk:

Or, in ssh:

 
# httpd -M |grep deflate

Then you need to create the file /etc/httpd/conf.d/deflate.conf


# vim /etc/httpd/conf.d/deflate.conf

and add the following into it.

 
<ifmodule mod_deflate.c>
AddOutputFilterByType DEFLATE text/html text/plain text/xml text/css text/javascript application/javascript
DeflateCompressionLevel 8
</ifmodule>

Restart Apache


/etc/init.d/httpd restart


Chech here – https://checkgzipcompression.com