Req: POST coap://[2001:db8:4::ff]/rd
  ?ep=grp_R2-4-015&et=core.rd-group&base=coap://[ff05::1]
Payload:
</light/left>;rt="tag:example.com,2020:light",
</light/middle>;rt="tag:example.com,2020:light",
</light/right>;rt="tag:example.com,2020:light"

Res: 2.01 Created
Location-Path: /rd/501