The cleaned backend removes the weakest parts of the original exercises.

Database settings are isolated in one file so credentials are not repeated across handlers.

return [
    'db_host' => '127.0.0.1',
    'db_port' => 3306,
    'db_name' => 'flowledger',
    'db_user' => 'root',
    'db_password' => '',
];

The create handler builds a normalized payload, validates it, prepares the SQL statement, then binds values in the expected column order.

$statement = $connection->prepare(
    'INSERT INTO customers
    (customer_id, first_name, last_name, gender, email, phone, address)
    VALUES (?, ?, ?, ?, ?, ?, ?)'
);

The listing page keeps the read query simple and focuses on returning a complete view of each customer record.

$result = $connection->query(
    'SELECT customer_id, first_name, last_name, gender, email, phone, address, created_at
     FROM customers
     ORDER BY created_at DESC'
);