What are some best practices for debugging PHP scripts that are executed in the background, such as PayPal IPN listeners?

When debugging PHP scripts that are executed in the background, such as PayPal IPN listeners, it is important to log any errors or messages to a file for later review. This can help identify any issues that may be causing the script to not function correctly. Additionally, using tools like Xdebug or setting up breakpoints can help step through the code and pinpoint where any errors may be occurring.

// Example of logging errors to a file
error_log("Error message", 3, "error.log");

// Example of using Xdebug to debug the script
xdebug_start_trace("trace_output");
// Code to debug
xdebug_stop_trace();