enable sflow on dell s series switch for Opmanager

I am trying to configure sflow on my S series S31XX switches to send flow data to OPManager, but seems to hit error.

OPManager not able to configure the switch and even if i manually configure on the switch, it does not work.

switch not added to OPManager for sflow.

sflow collector 172.16.xx.xx agent-addr 172.16.xx.xx max-datagram-size 400
sflow enable
sflow extended-switch enable
sflow polling-interval 60
sflow max-header-size extended