Create Azure EventHub Message in Azure Functions

Likely you're just missing the out keyword on your parameter. Below is a working WebHook function that declares an out string message parameter that is mapped to the EventHub output, and writes an EventHub message via message = "Test Message".

Because async functions can't return out parameters, I made this function synchronous (returning an object rather than Task<object>). If you want to remain async, rather than use an out parameter, you can instead bind to an IAsyncCollector<string> parameter. You can then enqueue one or more messages by calling the AddAsync method on the collector.

More details on the EventHub binding and the types it supports can be found here. Note that the other bindings follow the same general patterns.

#r "Newtonsoft.Json"

using System;
using System.Net;
using Newtonsoft.Json;

public static object Run(HttpRequestMessage req, out string message, TraceWriter log)
{
    string jsonContent = req.Content.ReadAsStringAsync().Result;
    dynamic data = JsonConvert.DeserializeObject(jsonContent);

    log.Info($"Webhook was triggered! Name = {data.first}");

    message = "Test Message";

    var res = req.CreateResponse(HttpStatusCode.OK, new {
        greeting = $"Hello {data.first} {data.last}!"
    });

    return res;
}