Hello @rohitshrma007
The screenshots you have provided are not related to the SiteGround Optimizer plugin but to the All-inclusive Security Solution by SiteGround.
The message usually indicates that the REST API on your site is not working as expected. This might be due to a conflict with another plugin or the currently active template. You could try disabling the other plugins one by one and see if this would resolve the issue. Restrictive .htaccess rules may also be responsible for this behavior so we recommend carefully inspecting any existing .htaccess files.
If your site is hosted with SiteGround it would be best to open a support request from your Client Area. That way we will have the required access to investigate the issue in more detail and provide a solution.
Best regards,
Georgi Ganchev