Just putting this on the NSO community, as I had trouble finding the answer. For a yang list which has a key which has a backslash in it, you need to put in special characters instead of the backslash:
instead of:
http://{{NSO_IP}}:{{NSO_HTTP_PORT}}/restconf/data/tailf-ncs:devices/device=netsim-ios-0/config/tailf-ned-cisco-ios:interface/FastEthernet=0/0
you would put:
http://{{NSO_IP}}:{{NSO_HTTP_PORT}}/restconf/data/tailf-ncs:devices/device=netsim-ios-0/config/tailf-ned-cisco-ios:interface/FastEthernet=0%2F0
cross-post, also see this post: https://community.cisco.com/t5/cisco-digital-network/interrogate-ios-xe-interfaces-with-restconf-with-postman/td-p/3463341