Added 3.5

FitConnect/Subscriber.cs

@@ -114,7 +114,17 @@ public class Subscriber : FitConnectClient,
             throw new SecurityEventException(problem);
         }
 
-        var schema = JsonSchema.FromUrlAsync(submission.Metadata?.Schema).Result;
+        JsonSchema? schema;
+        try {
+            schema = JsonSchema.FromUrlAsync(submission.Metadata?.Schema).Result;
+        }
+        catch (Exception e) {
+            // SuccessCriteria:3.5
+            var problem = new Problems(Problems.ProblemTypeEnum.UnsupportedSchema,
+                Problems.DetailUnsupportedSchema);
+            throw new SecurityEventException(problem, e);
+        }
+
         VerifyMetadata(submission, metadataString, schema);
 
         // SuccessCriteria:3.3