CREATE TABLE invoices (
    invoice_id INT AUTO_INCREMENT PRIMARY KEY,
    user_id INT,
    payment_id VARCHAR(255),
    payment_date DATETIME,
    amount DECIMAL(10, 2),
    usage_count INT,
    status ENUM('paid', 'unpaid') DEFAULT 'unpaid',
    FOREIGN KEY (user_id) REFERENCES users(user_id)
);
