Unknown web method getTrackingNumber. Parameter name: methodName

Question

I'm trying to call a function in my .aspx.cs, and it works fine until it is deployed. I have several method calls, but this is the only one giving me the 500 error. I've searched everywhere but can't seem to find an appropriate solution.

function NewEmail(){
    alertify.confirm('Envío de correo', 'El formulario de envío se abrirá en una nueva ventana', function () {
    $.ajax({
        type: 'POST',
        url: "Priority.aspx/getTrackingNumber",
        data: {},
        contentType: "application/json; charset=utf-8",
        dataType: "json",
        success: function (response) {
            //some code here
        }
    });
}, function () { alertify.error('Envío de correo cancelado') }).set('labels', { ok: 'Abrir formulario', cancel: 'Cancelar' });
}

and this is the code in my .aspx.cs file

[WebMethod, ScriptMethod(ResponseFormat = ResponseFormat.Json, UseHttpGet = false)]
public static string getTrackingNumber()
{
    //code here
}