Hi @LukeSmallwood ,
I managed to explore the fields, and there is a "CITY_NAME" field that I want to display as label.
const QString labelJson(R"({"labelExpressionInfo":{"expression":"$feature.CITY_NAME"},"labelPlacement":"esriServerPolygonPlacementAlwaysHorizontal","symbol":{"angle":0,"backgroundColor":[255,255,255,60],"borderLineColor":[255,255,0,255],"borderLineSize":1,"color":[255,255,0,255],"font":{"decoration":"none","size":8,"style":"normal","weight":"normal"},"haloColor":[255,255,255,120],"haloSize":0.5,"horizontalAlignment":"center","kerning":false,"type":"esriTS","verticalAlignment":"middle","xoffset":0,"yoffset":0}})");
However no labels are displayed on the feature layer.