connect to a pdb from a cdb

Hello,

cannot connect to a pdb from a cdb

SQL> show con_name

CON_NAME

------------------------------

CDB$ROOT

SQL>

SQL>

SQL> select count (*) from tableowner.tablename@pdbname;

select count (*) from tableowner.tablename@pdbname

                             *

ERROR at line 1:

ORA-01017: invalid username/password; logon denied

ORA-02063: preceding line from pdbname

however when connected on the pdb it's OK

SQL> alter session set container=pdbname;

Session altered.

SQL> select count (*) from tableowner.tablename@pdbname;

 COUNT(*)

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 143486696