ORA-01665: control file is not a standby control file when starting standby database after failover

When i was doing FAILOVER, it switched properly to other Server (Now Primary). When i tried to check standby server, i received ORA-01665: control file is not a standby control file

SQL> STARTUP MOUNT
ORACLE instance started.
Database mounted.
SQL> ALTER DATABASE RECOVER MANAGED STANDBY DATABASE DISCONNECT;
ERROR at line 1:
ORA-01665: control file is not a standby control file
SQL> SELECT database_role FROM v$database;
DATABASE_ROLE
—————-
PRIMARY

The steps i followed to solve this issue:
SQL> ALTER DATABASE CONVERT TO PHYSICAL STANDBY;
Database altered.
SQL> STARTUP MOUNT
ORACLE instance started.
Database mounted.
SQL> SELECT database_role FROM v$database;
DATABASE_ROLE
—————-
PHYSICAL STANDBY
SQL> ALTER DATABASE RECOVER MANAGED STANDBY DATABASE DISCONNECT;
Database altered.
If you are using DG Broker, then reinstate standby database using below command.
DGMGRL> reinstate database STDBY;

Also check if archives are being transferred to standby location from primary.