I AM CREATING CONSTRAINTS IN A TABLE

Question

CREATE TABLE ACTORS
(
    ACTOR_ID NUMBER(10),
    STAGE_NAME VARCHAR2(40) NOT NULL,
    FIRST_NAME VARCHAR2(25) NOT NULL,
    LAST_NAME VARCHAR2(25) NOT NULL,
    BIRTH_DATE DATE
);

ALTER TABLE ACTORS 
    ADD CONSTRAINTS PK_ACTOR_ID PRIMARY KEY(ACTOR_ID);

ALTER TABLE ACTORS 
    ADD CONSTRAINTS FK_ 
        FOREIGN KEY(STAR_BILLING_ID) REFERENCES STAR_BILLINGS(STAR_BILLING_ID);

CREATE TABLE STAR_BILLINGS
(
    ACTOR_ID NUMBER(10) NOT NULL,
    TITLE_ID NUMBER(10) NOT NULL,
    STAR_BILLING_ID INT GENERATED ALWAYS AS IDENTITY,
    COMMENTS VARCHAR2(40)
);

Error:

ORA-00904: "STAR_BILLING_ID": invalid identifier ORA-06512