What steps need to be taken to ensure that server-side includes work for counters and online user tracking in PHP?

To ensure that server-side includes work for counters and online user tracking in PHP, you need to enable the Server Side Includes (SSI) module in your web server configuration and ensure that PHP scripts are being parsed within SSI files. Additionally, you will need to create PHP scripts to handle the counting and tracking functionality, and include these scripts in your SSI files using the appropriate SSI syntax.

<!--#include virtual="/path/to/counter.php" -->
<!--#include virtual="/path/to/user_tracking.php" -->