RMAN-05503: at least one auxiliary channel must be allocated to execute this command

RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03002: failure of Duplicate Db command at 09/21/2021 02:31:10
RMAN-05501: aborting duplication of target database
RMAN-05503: at least one auxiliary channel must be allocated to execute this command
RMAN-05503: at least one auxiliary channel must be allocated to execute this command

RMAN> run
{
allocate channel c1 device type disk;
allocate channel c2 device type disk;
allocate channel c3 device type disk;
allocate auxiliary channel c4 device type disk;
2> 3> 4> duplicate target database for standby from active database using backupset section size 300M;
}