There has been a critical error on your website.
Please follow the instructions how to debug Wordpress to see the real error.
You can also check your log files of your server.
What have you configured?
Installed the plugin added purchase code and strted using short code
in error log it say -
[15-Dec-2020 17:55:33 UTC] PHP Parse error: syntax error, unexpected '') && !class_exists('' (T_CONSTANT_ENCAPSED_STRING) in /results/wp-content/plugins/advanced-iframe/includes/advanced-iframe-main-after-iframe.php on line 10
Try to reinstall the plugin. I have checked the code - In the one I uploaded to codecanyon there all looks fine.
Which version have you installed?
can you also simply post the line? In wordpress you can go to the plugin editor and navigate to the file. And then please post line 10.