PDB database is in restricted mode, not able to connect with the PDB database

Check the PDB is in restricted mode

select CON_ID,NAME,OPEN_MODE,RESTRICTED,OPEN_TIME from v$pdbs;

Check the error at PDB level:

select name, cause, type, message, status from pdb_plug_in_violations where type = 'ERROR' and status !='RESOLVED';

Error: PDB1 Sync Failure ERROR “Sync PDB failed with ORA-65177

Solution:

For fix this error: Delete the alter user statement from PDB_SYNC$ for both CDB and PDB

-- First connect with CDB database:

col NAME format a30
col SQLSTMT format a100
Select CTIME,SQLSTMT,NAME,FLAGS,OPCODE,REPLAY# from PDB_SYNC$ where SQLSTMT like '%alter user username%'

--If you find the row take a backup of row and delete with following query:
delete from PDB_SYNC$ where SQLSTMT like '%alter user username%';
commit;

--Connect with PDB database
ALTER SESSION SET CONTAINER=PDB1;

col NAME format a30
col SQLSTMT format a100
Select CTIME,SQLSTMT,NAME,FLAGS,OPCODE,REPLAY# from PDB_SYNC$ where SQLSTMT like '%alter user username%'

--If you find the row take a backup of row and delete with following query:
delete from PDB_SYNC$ where SQLSTMT like '%alter user username%';
commit;

Restart the PDB database:

SQL> alter session set container=CDB$ROOT;

SQL> alter pluggable database PDB close;
SQL> alter pluggable database PDB open;