diff --git a/README.md b/README.md
index 4d6234e..ee1f3d7 100644
--- a/README.md
+++ b/README.md
@@ -3,6 +3,8 @@
 To get up-and-running, install the node dependencies and start the server.
 🚀 Go to http://localhost:4000/ to play in the GraphQL Playground.
 
+Slides: https://app.box.com/s/6l6xi3mm26d7ur9g7n05egguc6dkyz3v
+
 ```
 npm i
 npm start
diff --git a/src/typeDefs.js b/src/typeDefs.js
index a6d424b..2247f4b 100644
--- a/src/typeDefs.js
+++ b/src/typeDefs.js
@@ -52,7 +52,7 @@ module.exports = gql`
   }
 
   input ReservationProductInput {
-    productId: String!
+    productId: ID
     quantity: Int
   }