I cannot complete the Subscribe to Platform Events challenge. When I click the 'Check Challenge' button I get the following error:

Publishing an Order_Event__e did not create the associated task successfully. Please check your trigger and event.

Here is my code:

trigger OrderEventTrigger on Order_Event__e (after insert) {
    // List to hold all tasks to be created.
    List<Task> tasks = new List<Task>();
    
    // Get queue Id for case owner
    String usr = UserInfo.getUserId(); 
        
       
    // Iterate through each notification.
    for (Order_Event__e event : Trigger.New) {
        if (event.Has_Shipped__c == true) {
            // Create Task to dispatch new team.
            Task t = new Task();
            t.Priority = 'Medium';
            t.Status = 'New';
            t.Subject = 'Follow up on shipped order' + event.Order_Number__c;
            t.OwnerId = Usr;
            tasks.add(t);
        }
   }
    
    // Insert all tasks corresponding to events received.
    insert tasks;
}

Please assist. Thanks.