How can inconsistent variable naming conventions impact the functionality of PHP code?

Inconsistent variable naming conventions can impact the functionality of PHP code by causing confusion and making the code harder to read and maintain. It can lead to errors when trying to reference variables with different naming styles. To solve this issue, developers should establish a standardized naming convention and adhere to it consistently throughout their codebase.

// Example of using a consistent variable naming convention
$firstName = "John";
$lastName = "Doe";

echo $firstName . " " . $lastName;