This notification is usually the result of a slow server and results in a server-side timeout. You can check your server and page speed at any time with the Google page speed test. Besides that, there are several solutions for this request:
System requirements for Blog2Social
Please make sure that your website meets the system requirements for Blog2Social.
If your hoster provides a server hosted caching and activated "nginx caching" it might result in a "connection to the server failed" message. This happens due to incorrect DNS settings on the part of the hoster, resulting in a 504 error-notification. Please contact your hoster in this case in order to solve the request.
Increase your max execution time
Please change the max execution time in your .htaccess File (in the root folder of WordPress) to 40 or highger: "php_value max_execution_time 40"
You can also use the WordPress plugin "WP Maximum Execution Time exceeded" for this: https://wordpress.org/plugins/wp-maximum-execution-time-exceeded/
If you use an additional Firewall, please make sure that your settings allow outgoing connections or include an exeption or whitelisting for Blog2Social.