Here's a top to bottom test case from my cloud account.... Compare and contrast to yours and see what's different. (You didn't give us any output so we can't really see what you're doing)
SQL> CREATE TABLE customers
2 (
3 cust_id NUMBER NOT NULL,
4 cust_first_name VARCHAR2(20) NOT NULL,
5 cust_last_name VARCHAR2(40) NOT NULL,
6 cust_gender CHAR(1) NOT NULL,
7 cust_year_of_birth NUMBER(4) NOT NULL,
8 cust_marital_status VARCHAR2(20),
9 cust_street_address VARCHAR2(40) NOT NULL,
10 cust_postal_code VARCHAR2(10) NOT NULL,
11 cust_city VARCHAR2(30) NOT NULL,
12 cust_city_id NUMBER NOT NULL,
13 cust_state_province VARCHAR2(40) NOT NULL,
14 cust_state_province_id NUMBER NOT NULL,
15 country_id NUMBER NOT NULL,
16 cust_main_phone_number VARCHAR2(25) NOT NULL,
17 cust_income_level VARCHAR2(30),
18 cust_credit_limit NUMBER,
19 cust_email VARCHAR2(50),
20 cust_total VARCHAR2(14) NOT NULL,
21 cust_total_id NUMBER NOT NULL,
22 cust_src_id NUMBER,
23 cust_eff_from DATE,
24 cust_eff_to DATE,
25 cust_valid VARCHAR2(1),
26 CONSTRAINT customers_pk PRIMARY KEY (cust_id)
27 );
Table created.
SQL> begin
2 dbms_cloud.create_credential (
3 credential_name => 'OBJ_STORE_DB_BUCKET',
4 username => 'OracleIdentityCloudService/myusername@mydomain.com',
5 password => 'myauthkey'
6 ) ;
7 end;
8 /
PL/SQL procedure successfully completed.
SQL>
SQL>
SQL> select *
2 from dbms_cloud.list_objects(
3 credential_name => 'OBJ_STORE_DB_BUCKET',
4 location_uri => 'https://objectstorage.~~~~~~oraclecloud.com/n/~~~~~~~~~~~~~/o/');
OBJECT_NAME BYTES CHECKSUM CREATED LAST_MODIFIED
------------- ---------- ----------------------------------- ----------------------------------- -----------------------------------
customers.csv 12671219 2704544fb343dc50728bb09bdd6fbcbb 25-SEP-25 06.43.49.986000 AM +00:00
SQL> BEGIN
2 DBMS_CLOUD.copy_data(
3 table_name => 'CUSTOMERS',
4 credential_name => 'OBJ_STORE_DB_BUCKET',
5 file_uri_list => 'https://objectstorage.~~~~~~~~.oraclecloud.com/n/~~~~~~~~~~~~~~~/o/customers.csv',
6 format => json_object('ignoremissingcolumns' value 'true',
7 'removequotes' value 'true',
8 'delimiter' value ',',
9 'skipheaders' value 1,
10 'dateformat' value 'yyyy-mm-dd')
11 );
12 END;
13 /
PL/SQL procedure successfully completed.