Could you post more details? some code sample both ajax and c#?

Just to be more clear what you are trying to achieve.

Just in case you if are trying to make a "post" you should decorate your endpoint with [HttpPost] as the HttpGet is the default method

Here is the JavaScript to call the controller in my view:

<script>
$('#newUser').submit(function (e) {
    e.preventDefault();
    var user = $("#user").val();
    var password = $("password").val();
    $.get("/umbraco/api/userManager/createUser/" + user + "/" + password);
});

And here is the method in my controller:

[HttpGet()]
    [Route("createUser/{user}/{password}")]
    public void createUser(string user, string password)
    {
        Helper.GetUserDetails(user);
    }

This is just to get it working, once it is working it will be totally different.

Try these 4 things.

1 . Because of your

[Route("createUser/{user}/{password}")]

I think the url should be like that but I may be wrong.

$.get("/umbraco/api/createUser/" + user + "/" + password);

2 . Try add the full Url in your get method just in case...

$.get("{yourDomain}/umbraco/api/userManager/createUser/" + user + "/" + password);

3 .add [FromUri] to parameters

public void createUser([FromUri]string user, [FromUri]string password)

4 . remove the [Route] and do that to ajax

$.get("{yourDomain}/umbraco/api/userManager/createUser?user=" + user + "&password=" + password);

and your controller should look like that

[HttpGet]
public void createUser([FromQuery]string user, [FromQuery]string password)

Eventually I believe you need to do an HttpPost as you want to create an account

In that case your controller should look like that

[HttpPost]
public void CreateUser([FromBody]RegisterModel model)

and your ajax should look like something that

$.ajax({
    url: '{yourDomain}/umbraco/api/userManager/createUser,
    type: 'POST',
    data: ({ User: user, Password: password }),
    contentType: 'application/json; charset=utf-8',
    dataType: 'json',
    async: false,
    cache: false,
    success: function (result) {

    },
    error: function (xhr, ajaxOptions, thrownError) {
        alert(xhr.status);
  }
});

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