Let us start here, from square one. No, from Zero!

api/resources/dart/spiceapi/src/exceptions.dart

@@ -0,0 +1,11 @@
+part of spiceapi;
+
+class APIError implements Exception {
+  String cause;
+  APIError(this.cause);
+
+  @override
+  String toString() {
+    return this.cause;
+  }
+}