APEX

I need to do a HTTPS POST to a endpoint for authentication. After that I can do a GET. I need to add some headers as well and I think this is the problem.

Firstly I generate the XML, I've tested this in Postman and the XML is valid.

Secondly I add the headers:

-- Set the request headers
  apex_web_service.g_request_headers(1).name := 'Content-Type';
  apex_web_service.g_request_headers(1).value := 'application/xml';
  apex_web_service.g_request_headers(2).name := 'x-rs-key';
  apex_web_service.g_request_headers(2).value := '<key>';
  apex_web_service.g_request_headers(3).name := 'Host';
  apex_web_service.g_request_headers(3).value := '<host>';

Then I do the HTTPS request:

  -- Set the HTTPS request
  l_http_resp := apex_web_service.make_rest_request(
    p_url         => l_auth_url,
    p_http_method => 'POST',
    p_body_blob   => l_request_object
  );

l_request_object =

<?xml version="1.0" encoding="UTF-8" ?>
 <AuthenticationCredentials xmlns:i="http://www.w3.org/2001/XMLSchema-instance">
  <UserName>{USERNAME}</UserName>
  <Password>{PASSWORD}</Password>
  <AuthenticationType>SetCookie</AuthenticationType>
  <AuthenticationOptions>None</AuthenticationOptions>
  <AuthenticationChallangeResponse i:nil="true" />
  <ClientDeviceDescription i:nil="true" />
 </AuthenticationCredentials>

I've tested this all in Postman and it works fine, but if I leave some headers out I get the same 500 interal error. Does somebody now what I do wrong?

I've also tried using the following format but no success either:

apex_web_service.set_request_headers(
        p_name_01        => 'Content-Type',
        p_value_01       => 'application/xml',
        p_name_02        => 'x-rs-key',
        p_value_02       => '<key>'
        p_name_02 		 => 'Host',
		p_value_02 	     => '<host>');

When I change the Host value in Postman I get a error code 500 as well, but I checked and the hosts is exactly the same value in my script.