What is the error message "App Domains: ... should not contain protocol information" indicating in PHP Facebook App registration?

The error message "App Domains: ... should not contain protocol information" indicates that the domain specified in the Facebook App settings should not include the protocol (like http:// or https://). To solve this issue, simply provide the domain name without the protocol information.

// Incorrect way with protocol information included
$appDomains = array('http://example.com', 'https://example.com');

// Correct way without protocol information
$appDomains = array('example.com');