The WAN Edges send relevant alarms and events to vManage and you can use an API to query these from vManage. https://www.cisco.com/c/en/us/td/docs/routers/sdwan/configuration/Monitor-And-Maintain/monitor-maintain-book/m-alarms-events-logs.html You ma...

It's the interface usage (both rx and tx) of all WAN interfaces in VPN 0. In Mbps, over the last 24 hours.

If you are trying to do this under Cisco SD-WAN, see https://sdwan-docs.cisco.com/Product_Documentation/Software_Features/Release_18.4/07Policy_Applications/01Application-Aware_Routing