Tried to add a service to a database, but it failed with ORA-44303.
SQL> exec dbms_service.create_service('ERPAPP1', 'ERPAPP1');
BEGIN dbms_service.create_service('ERPAPP1', 'ERPAPP1'); END;
ERROR at line 1:
ORA-44303: service name exists
ORA-06512: at "SYS.DBMS_SERVICE_ERR", line 21
ORA-06512: at "SYS.DBMS_SERVICE", line 316
ORA-06512: at line 1
ORA-44303 means that the service name you tried to create has been used in the database, you may choose another name to create the service or modify the current service to fit your requirements.
Another possibility is that you connected to a wrong database server, please check your connection string for sure.