Update index.md

Author: joeynmq

src/connections/destinations/catalog/actions-klaviyo/index.md

@@ -114,4 +114,8 @@ If this approach doesn't address your use case, [reach out to Segment](mailto:fr
 
 ### Can batching be enabled for the entire Klaviyo (Actions) destination?
 
-Batching is only available for events sent through the Upsert Profile action mapping. Other actions in the Klaviyo (Actions) destination don't support batching.
+Batching is only available for events sent through the Upsert Profile action mapping. Other actions in the Klaviyo (Actions) destination don't support batching.
+
+### Why can't I see custom Profile Properties being passed to Klaviyo?
+
+Klaviyo's API supports only [Klaviyo default properties](https://help.klaviyo.com/hc/en-us/articles/115005074627#h_01HA32RZBASB9K0AQHHD8MHM3C) as Profile Properties. Any custom properties that are not included in this predefined list will be silently dropped and will not be added to the user's profile.