Please update the coding to current standards.

This plugin is still using a function that has been deprecated since WP 4.5.0 was released on April 12th, 2016. So that is now more than 3 years ago. ??

Please replace /includes/shortcode.php line 17 from
get_currentuserinfo(); to the correct wp_get_current_user();

The use of this old function floods error logs.

Also, it is not unlikely that after a certain period WordPress will remove get_currentuserinfo(); all together – breaking the plugin.

Also, line 40 in that same file gives a PHP warning:
Undefined index: HTTP_X_FORWARDED_PROTO in /wp-content/plugins/supersaas-appointment-scheduling/includes/shortcode.php on line 40

Could you please correct these and release an update?
Thank you! ??