Hi @Anonymous User, I'm tying to figure out where I would assign the "dt" variable within my dictionary. See Expression below. I'm having the same issue, in which the "CloseOutDate" field is not populating.
var portal = Portal("https://cms.maps.arcgis.com/"); 
var TandJSoft = FeatureSetByPortalItem(portal,"c6366ef0c8424130a76e9e9d08f292de",0,["*"],false); 
var JWSoft = FeatureSetByPortalItem(portal,"92497f50542248dcb798d091dd18d004",0,["*"],false); 
var start = ToLocal(Date(1970,0,01,0,0,0,0))
var dt = DateDiff(Now(), start, 'milliseconds')
var combinedDict = { 
  'fields': [ 
    { name: "Contractor", type:"esriFieldTypeString" },
    { name: "Total", type: "esriFieldTypeDouble" },
    { name: "Address", type: "esriFieldTypeString" }, 
    { name: "ProjectName", type: "esriFieldTypeString" },
    {name: "Status", type: "esriFieldTypeString" },
    {name: "CloseOutDate", type: "esriFieldTypeDate" },
  ], 
  geometryType: "", 
  features: [], 
};
var i = 0; 
// Loop through each FeatureSet and store its attributes 
for (var t in TandJSoft) { 
  combinedDict.features[i++] = { 
    attributes: {
      Contractor: t["Contractor"],
      Total: t["Total"],
      Address: t["Address"], 
      ProjectName: t["ProjectName"],
      Status: t["Status"],
      CloseOutDate: t["CloseOutDate"],
    }, 
  }; 
} 
for (var m in JWSoft) { 
  combinedDict.features[i++] = { 
    attributes: { 
      Contractor: m["Contractor"],
      Total: m["Total"],
      Address: m["Address"], 
      ProjectName: m["ProjectName"],
      Status: m["Status"],
      CloseOutDate: m["CloseOutDate"],
    }, 
  }; 
}
// Return dictionary cast as a FeatureSet  
return FeatureSet(Text(combinedDict));