Как исправить эту ошибку "ошибка: нет уникального ограничения, соответствующего заданным ключам для ссылочной таблицы "инвентаризация""

CREATE TABLE INVENTORY(
    machine_name VARCHAR(25) UNIQUE,
    --ip_address WILL NEVER BE LONGER THAN 15 CHARACTERS BASED OF THE IP ADDRESS FORMAT
    ip_address CHAR(15) NOT NULL,
    --network_port WILL NEVER BE LONGER THAN 6 CHARACTERS BASED OF THE NETWORK PORT FORMAT
    network_port CHAR(6) NOT NULL,
    --mac_address WILL NEVER BE LONGER THAN 17 CHARACTERS BASED OF THE MAC ADDRESS FORMAT
    mac_address CHAR(17) NOT NULL,
    location_id VARCHAR(3) NOT NULL,
    CONSTRAINT pk_INVENTORY PRIMARY KEY(machine_name,ip_address, network_port, mac_address),
    CONSTRAINT fk_INVENTORY FOREIGN KEY (location_id) REFERENCES LOCATIONS(location_id)
                            ON DELETE CASCADE ON UPDATE CASCADE
);
CREATE TABLE TICKETS(
    ticket_number INT,
    owner_pplSoft INT NOT NULL,
    date_submitted DATE NOT NULL,
    date_closed DATE NOT NULL,
    --DATEDIFF() WILL BE USED HERE TO GET THE INT VALUE
    days_worked_on INT NOT NULL,
    category_id INT NOT NULL,
    machine_name VARCHAR(25) NOT NULL,
    location VARCHAR(10) NOT NULL,
    description VARCHAR(280),
    CONSTRAINT pk_TICKETS PRIMARY KEY(ticket_number),
    CONSTRAINT fk_1_TICKETS FOREIGN KEY (owner_pplSoft) REFERENCES USERS(pplSoft)
                            ON DELETE CASCADE ON UPDATE CASCADE,
    CONSTRAINT fk_2_TICKETS FOREIGN KEY (category_id) REFERENCES CATEGORIES(category_id)
                            ON DELETE CASCADE ON UPDATE CASCADE,
    CONSTRAINT fk_3_TICKETS FOREIGN KEY (machine_name) REFERENCES INVENTORY(machine_name)
                            ON DELETE CASCADE ON UPDATE CASCADE,
    CONSTRAINT fk_4_TICKETS FOREIGN KEY (location) REFERENCES LOCATIONS(location)
                            ON DELETE CASCADE ON UPDATE CASCADE
);