Bad request when posting to OData Data Entity in Dynamics 365 - post

Question

I've created a public Data Entity in dynamics with the following fields:
I keep getting a bad request response, but I'm not sure why.
I've tried to make a POST request in two ways:
1.
HireAction hireAction = new HireAction() { CompanyName = "DEMF", MovieId = "DEMF-000000014", HireActionStatus = "Created" };
string jsonMessage = JsonConvert.SerializeObject(hireAction);
using (HttpClient client = new HttpClient())
{
HttpRequestMessage requestMessage = new
HttpRequestMessage(HttpMethod.Post, "MyDynamicsEnvironmentName/data/HireActions?cross-company=true");
requestMessage.Content = new StringContent(jsonMessage, Encoding.UTF8, "application/json");
requestMessage.Headers.Add("Authorization", AuthResult.AuthorizationHeader);
HttpResponseMessage response = client.SendAsync(requestMessage).Result;
if (response.StatusCode == System.Net.HttpStatusCode.OK)
{
//Logic
}
}
var url = "MyDynamicsEnvironmentName/data/HireActions?cross-company=true";
var req = HttpWebRequest.Create(url);
req.Method = "POST";
req.ContentType = "application/json";
req.Headers["Authorization"] = AuthResult.AuthorizationHeader;
HireAction hireAction = new HireAction() { CompanyName = "DEMF", MovieId = "DEMF-000000014", HireActionId = "12345", HireActionStatus = "Created" };
var jsonSettings = new JsonSerializerSettings
{
DateTimeZoneHandling = DateTimeZoneHandling.Local
};
var postString = "CompanyName='DEMF'" + "&MovieId='DEMF-000000014'" + "&HireActionId=132&HireActionStatus='Created'";
var data = JsonConvert.SerializeObject(postString, jsonSettings);
var bytes = Encoding.Default.GetBytes(postString);
var newStream = req.GetRequestStream();
newStream.Write(bytes, 0, bytes.Length);
newStream.Close();
using (var resp = req.GetResponse())
{
var results = new StreamReader(resp.GetResponseStream()).ReadToEnd();
}
Some keypoints:
-Of course you'd replace MyDynamicsEnvironmentName with the URL for the environment. The URL is correct and verified however, by the fact that GET requests do work
-The Authresult.AuthorizationHeader contains a valid token, also validated by working GET requests
As said before, both of these result in a bad request. Does someone know what is wrong or missing?