Why does this C# connector code throw an error at topic creation?

I'm still trying to grasp my head around how the C# connector works.

I made a custom type in the XML, tried to make a subscriber of that type, and the C# app just crashes at the line where DomainParticipant.CreateTopic is called.

I just don't understnad why.

namespace MyExample {

   public static class MyExampleSubscribe {
      private static int ProcessData(DataReader<DynamicData> reader) {

         int samplesRead = 0;
         using var samples = reader.Take();
         foreach (var sample in samples.ValidData) {
            Console.WriteLine($"Received: {sample}");
            samplesRead++;
         }

         return samplesRead;
      }

      public static void Main (int domainId = 0, int sampleCount = 10) {

         // A DomainParticipant allows an application to begin communicating in
         // a DDS domain. Typically there is one DomainParticipant per application.
         // DomainParticipant QoS is configured in USER_QOS_PROFILES.xml
         //
         // A participant needs to be Disposed to release middleware resources.
         // The 'using' keyword indicates that it will be Disposed when this
         // scope ends.

         using DomainParticipant participant = DomainParticipantFactory.Instance
         .CreateParticipant(domainId);

         // A Topic has a name and a datatype. Create dynamically-typed
         // Topic named "MyExample Topic" with the type definition of
         // "MyExample" in MyExample.xml. To get the type we use a QosProvider

         var provider = new QosProvider("MyExample.xml");
         Topic<DynamicData> topic = participant.CreateTopic(
            "SuperData",
            provider.GetType("SuperData")
         );

         Subscriber subscriber = participant.CreateSubscriber();

         DataReader<DynamicData> reader = subscriber.CreateDataReader(topic);

         var statusCondition = reader.StatusCondition;
         statusCondition.EnabledStatuses = StatusMask.DataAvailable;
         int samplesRead = 0;
         statusCondition.Triggered += _ => samplesRead += ProcessData(reader);

         var waitset = new WaitSet();
         waitset.AttachCondition(statusCondition);

         while (samplesRead < sampleCount) {
            Console.WriteLine("MyExample subscriber sleeping for 4 sec...");
            waitset.Dispatch(Duration.FromSeconds(4));
         }
      }
   }
}

   <types>
      <!-- Define your types here -->

      <struct name="SuperData">
         <member name="msg" stringMaxLength="256" type="string" />
      </struct>
   </types>