ORA-16433: The database or pluggable database must be opened in read/write mode

Error
Oracle 12c version with PDBS database, Snapshot Standby Will not Convert to Physical Standby
While troubleshooting a tempfile issue, I convert the database to a snapshot standby.
When I attempted to covert the database back to physical standby, I recieved the following error:

alter database convert to physical standby;
*
ERROR at line 1:
ORA-16433: The database or pluggable database must be opened in read/write mode.


On checking pluggable database is currently mounted.

SYS@DBSERVER 07-NOV-18> show pdbs

CON_ID CON_NAME OPEN MODE RESTRICTED
---------- ------------------------------ ---------- ----------
2 PDB$SEED MOUNTED
3 CFGPDB1 MOUNTED


Solution
For converting the Snapshot Standby Database to Physical Standby Database. Database Should be in open state.

1) Open the Container database:
alter database open ;

2) Open all pluggable database:
alter pluggable database all open;

3) Check all pdbs are open in read write state:

show pdbs

CON_ID CON_NAME OPEN MODE RESTRICTED
---------- ------------------------------ ---------- ----------
2 PDB$SEED READ ONLY NO
3 CFGPDB1 READ WRITE NO


4) Check the CDB DATABASE ROLE

select name, db_unique_name, database_role, open_mode from v$database;

NAME DB_UNIQUE_NAME DATABASE_ROLE OPEN_MODE
--------- ------------------------------ ---------------- --------------------
SVCFG1 svcfg1rmt SNAPSHOT STANDBY READ WRITE

Note: It is in snapshot standby role with READ/WRITE mode, then you should now be able to convert it back to physical standby.

5) Shutdown the Database.

SQL> SHUTDOWN IMMEDIATE; 


6) Mount the Database

SQL> STARTUP MOUNT; 


7) Convert Snapshot Standby to Physical Standby

SQL> ALTER DATABASE CONVERT TO PHYSICAL STANDBY; 


8) Shutdown the Database

SQL> SHUTDOWN IMMEDIATE; 


9) Startup in Nomount mode

SQL> STARTUP NOMOUNT; 


10) Mount the Physical Standby Database

SQL> ALTER DATABASE MOUNT STANDBY DATABASE; 

--Verify
select open_mode,database_role from v$database;
OPEN_MODE DATABASE_ROLE
---------- ----------------
MOUNTED PHYSICAL STANDBY


11) Start Redo Log Apply

SQL> ALTER DATABASE RECOVER MANAGED STANDBY DATABASE THROUGH ALL SWITCHOVER DISCONNECT USING CURRENT LOGFILE;