It seems like the lack of privileges for me. Often a PUBLIC user has an EXECUTE privilege on this package, but the privilege can be revoked.
You can check if PUBLIC this privilege by running the following query:
SELECT * FROM all_tab_privs WHERE grantee = 'PUBLIC' AND table_name = 'UTL_FILE';
If there are no returned rows, try granting the execution privilege either to the user you registered with, or, or PUBLIC , as some privileged user, for example SYS :
GRANT EXECUTE ON SYS.utl_file TO user_name;
Edit
You must grant this privilege during registration, for example, SYS user.
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