Scan SNMP Ocs inventory found nothing

Hello

Having already uploaded my workstations by the agent, I would like to upload my switches and printers with the SNMP options on ocs inventory.

I looked at the doc and some tuto I added the IP range to activate the SNMP and configure the settings on the web interface but nothing is displayed. And there's a connection to an agent for SNMP?

If you can help me, it would be nice
Thank you in advance