diff --git a/15.md b/15.md
index edece81..68d28ff 100644
--- a/15.md
+++ b/15.md
@@ -88,7 +88,7 @@ Fields that are not self-explanatory:
     "images": <[String], array of image URLs, optional>,
     "currency": <String, currency used>,
     "price": <float, cost of product>,
-    "quantity": <int, available items>,
+    "quantity": <int or null, available items>,
     "specs": [
         [<String, spec key>, <String, spec value>]
     ],
@@ -102,6 +102,7 @@ Fields that are not self-explanatory:
 ```
 
 Fields that are not self-explanatory:
+ - `quantity` can be null in the case of items with unlimited abailability, like digital items, or services
  - `specs`:
    - an optional array of key pair values. It allows for the Customer UI to present product specifications in a structure mode. It also allows comparison between products
    - eg: `[["operating_system", "Android 12.0"], ["screen_size", "6.4 inches"], ["connector_type", "USB Type C"]]`