What is the potential risk of relying solely on user input to determine if a payment has been made on a PHP website?

Relying solely on user input to determine if a payment has been made on a PHP website can pose a significant security risk. Users could potentially manipulate the input data to falsely indicate that a payment has been made when it has not. To mitigate this risk, it is crucial to validate the payment status with a secure and reliable payment gateway or backend system to ensure the accuracy of the information.

// Example of validating payment status with a secure payment gateway
$payment_status = $_POST['payment_status']; // Assuming this is the user input for payment status

// Validate payment status with a secure payment gateway
if($payment_status == 'paid') {
    // Process payment and update database
    // Additional verification steps can be added here
} else {
    // Handle invalid payment status
    echo "Invalid payment status";
}