full-sample.json

{
   "$schema":"https://schema.management.azure.com/providers/Microsoft.Logic/schemas/2015-08-01-preview/workflowdefinition.json#",
   "actions":{
      "Http":{
         "conditions":[
            {
               "dependsOn":"Values_GetJsonString"
            }
         ],
         "foreach":"@Json(body('Values_GetJsonString')).employees",
         "inputs":{
            "body":"@triggerBody()['firstName']",
            "method":"POST",
            "uri":"http://requestb.in/17jmsnu1"
         },
         "type":"Http"
      },
      "Values_GetJsonString":{
         "conditions":[

         ],
         "inputs":{
            "method":"get",
            "uri":"https://{mywebservice}.azurewebsites.net:443/api/Values/GetJsonString"
         },
         "metadata":{
            "apiDefinitionUrl":"https://{mywebservice}.azurewebsites.net/swagger/docs/v1",
            "swaggerSource":"website"
         },
         "type":"Http"
      }
   },
   "contentVersion":"1.0.0.0",
   "outputs":{

   },
   "parameters":{

   },
   "triggers":{
      "manual":{
         "inputs":{
            "schema":{
               "properties":{

               },
               "required":[

               ],
               "type":"object"
            }
         },
         "type":"Manual"
      }
   }
}

jsonresponse.cs

public HttpResponseMessage GetJsonString()
{
  var resp = new HttpResponseMessage(HttpStatusCode.OK)
  {
    Content = new StringContent(Generic.JsonString, Encoding.UTF8, "text/plain")
  };
  
  return resp;
}

sample-json.json

"Http": {
    "conditions": [
         {
            "dependsOn": "Values_GetJsonString"
        }
     ],
     "foreach": "@Json(body('Values_GetJsonString')).employees",
     "inputs": {
        "body": "@triggerBody()['firstName']",
        "method": "POST",
        "uri": "http://requestb.in/17jmsnu1"
     },
     "type": "Http"
}