What potential pitfalls can arise when trying to force lowercase usernames in PHP?

One potential pitfall when trying to force lowercase usernames in PHP is that it may lead to inconsistencies in data entry if users are allowed to input their own usernames. To solve this issue, you can use the strtolower() function in PHP to convert all usernames to lowercase before storing them in the database.

$username = strtolower($_POST['username']);
// Store the lowercase username in the database