What is wrong with this 'ALTER TABLE' command?

Question

Here is the command;

ALTER TABLE product 
    ADD CONSTRAINT prod_cust_fk 
        FOREIGN KEY (cust_id) REFERENCES  customer (cust_id) ENABLE;

ALTER TABLE product 
    ADD CONSTRAINT prod_sto_fk 
        FOREIGN KEY (sto_id) REFERENCES  bakery (sto_id) ENABLE;

ALTER TABLE product 
    ADD CONSTRAINT prod_sup_fk 
        FOREIGN KEY (sup_id) REFERENCES  supplier (sup_id) ENABLE;

CREATE INDEX prod_cust_ix ON product (cust_id);
CREATE INDEX prod_sto_ix ON product (sto_id);
CREATE INDEX prod_sup_ix ON product (sup_id);

The result:

"ORA-01735: invalid ALTER TABLE option
ORA-06512: at "SYS.WWV_DBMS_SQL_APEX_210200", line 673

ORA-06512: at "SYS.DBMS_SYS_SQL", line 1658
ORA-06512: at "SYS.WWV_DBMS_SQL_APEX_210200", line 659
ORA-06512: at "APEX_210200.WWV_FLOW_DYNAMIC_EXEC", line 1829

REFERENCES bakery (sto_id) ENABLE;

ALTER TABLE product ADD CONSTRAINT prod_sup_fk FOREIGN KEY (sup_id) REFERENCES supplier (sup_id) ENABLE;

CREATE INDEX prod_cust_ix ON product (cust_id);

CREATE INDEX prod_sto_ix ON product (sto_id);"

The table product

CREATE TABLE product
(
   prod_id    VARCHAR2(10) CONSTRAINT prod_id_nn NOT NULL ENABLE,
   prod_price NUMBER(3, 2) CONSTRAINT prod_price_nn NOT NULL ENABLE,
   prod_avail VARCHAR2(20) CONSTRAINT prod_avail_nn NOT NULL ENABLE,
   prod_mdate DATE CONSTRAINT prod_mdate_nn NOT NULL ENABLE,
   prod_edate DATE CONSTRAINT prod_edate_nn NOT NULL ENABLE,
   cust_id    NUMBER(4, 0),
   sto_id     VARCHAR(8) CONSTRAINT sto_id_nn NOT NULL ENABLE,
   sup_id     VARCHAR(10),

   CONSTRAINT prod_id_pk PRIMARY KEY (prod_id) USING INDEX ENABLE,
   CONSTRAINT prod_date_interval CHECK (prod_edate > prod_mdate) ENABLE

Table customer

CREATE TABLE  customer
(
    cust_id NUMBER(4,0) CONSTRAINT cust_id_nn NOT NULL ENABLE,
    cust_name VARCHAR2(500),
    cust_phone NUMBER(20),
    cust_add VARCHAR2(1000),
    cust_email VARCHAR2(400),
    CONSTRAINT customer_cust_id_pk PRIMARY KEY (cust_id) ENABLE 
);

Table bakery

CREATE TABLE bakery
(
     sto_id VARCHAR(8),
     sto_phone NUMBER(20) CONSTRAINT sto_phone_nn NOT NULL ENABLE,
     sto_add VARCHAR2(500) CONSTRAINT sto_add_nn NOT NULL ENABLE,
     sto_email VARCHAR2(400) CONSTRAINT sto_email_nn NOT NULL ENABLE,
     CONSTRAINT sto_id_pk PRIMARY KEY (sto_id) USING INDEX  ENABLE
);

Table supplier

CREATE TABLE supplier
(
    sup_id VARCHAR2(10) CONSTRAINT sup_id_nn NOT NULL ENABLE,
    sup_name VARCHAR2(500) CONSTRAINT sup_name_NN NOT NULL ENABLE,
    sup_add VARCHAR2(500) CONSTRAINT sup_add_nn NOT NULL ENABLE,
    CONSTRAINT sup_id_pk PRIMARY KEY (sup_id) USING INDEX  ENABLE
);

I'm using Oracle APEX 21.2.0