GZip leading to Error 500

@droidafrica The rules looks good, do you have any other rules inside your .htaccess besides default WordPress rules, if yes can you please remove other rules and keep only default WordPress rules and WP-optimize rules and check if it works?

Thanks for the reply @bornforphp
Just to avoid back and fort communication, I have included the the other content of my .htaccess

# BEGIN iThemes Security - Do not modify or remove this line
# iThemes Security Config Details: 2
	# Pass through Authorization header.
	<IfModule mod_rewrite.c>
		RewriteEngine On
		RewriteCond %{HTTP:Authorization} ^(.*)
		RewriteRule .* - [e=HTTP_AUTHORIZATION:%1]
	</IfModule>

	# Ban Hosts - Security > Settings > Banned Users
	SetEnvIF REMOTE_ADDR "^2a01:0?e0a:0?4e0:bce0:dd24:fcac:4a4a:6cc3$" DenyAccess
	SetEnvIF X-FORWARDED-FOR "^2a01:0?e0a:0?4e0:bce0:dd24:fcac:4a4a:6cc3$" DenyAccess
	SetEnvIF X-CLUSTER-CLIENT-IP "^2a01:0?e0a:0?4e0:bce0:dd24:fcac:4a4a:6cc3$" DenyAccess

	SetEnvIF REMOTE_ADDR "^2a01:0?e0a:0?4e0:bce0:8c94:6c6c:6bfc:0?dba$" DenyAccess
	SetEnvIF X-FORWARDED-FOR "^2a01:0?e0a:0?4e0:bce0:8c94:6c6c:6bfc:0?dba$" DenyAccess
	SetEnvIF X-CLUSTER-CLIENT-IP "^2a01:0?e0a:0?4e0:bce0:8c94:6c6c:6bfc:0?dba$" DenyAccess

	<IfModule mod_authz_core.c>
		<RequireAll>
			Require all granted
			Require not env DenyAccess
			Require not ip 2a01:e0a:4e0:bce0:dd24:fcac:4a4a:6cc3
			Require not ip 2a01:e0a:4e0:bce0:8c94:6c6c:6bfc:dba
		</RequireAll>
	</IfModule>
	<IfModule !mod_authz_core.c>
		Order allow,deny
		Allow from all
		Deny from env=DenyAccess
		Deny from 2a01:e0a:4e0:bce0:dd24:fcac:4a4a:6cc3
		Deny from 2a01:e0a:4e0:bce0:8c94:6c6c:6bfc:dba
	</IfModule>
# END iThemes Security - Do not modify or remove this line

# BEGIN WordPress
# The directives (lines) between "BEGIN WordPress" and "END WordPress" are
# dynamically generated, and should only be modified via WordPress filters.
# Any changes to the directives between these markers will be overwritten.
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>

# END WordPress

As you can see, aside WP default, the other code in the .htaccess is generated by iTheme security plugin.
Thanks for reviewing

@droidafrica Can you please keep only default WordPress rules and remove iThemes rules and then try to click Gzip and check if it works?

# BEGIN WordPress
# The directives (lines) between "BEGIN WordPress" and "END WordPress" are
# dynamically generated, and should only be modified via WordPress filters.
# Any changes to the directives between these markers will be overwritten.
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>

# END WordPress

I just did this, but still got same server error 500

@droidafrica

Could you send me a copy of your server’s Apache log?
If you are unsure where to find the PHP Error log, you can ask your hosts to provide it.

Can you also share your Site url?