diff --git a/src/main/java/org/gcube/social_networking/socialnetworking/model/beans/catalogue/CatalogueEvent.java b/src/main/java/org/gcube/social_networking/socialnetworking/model/beans/catalogue/CatalogueEvent.java
index 30e8398..d668a8c 100644
--- a/src/main/java/org/gcube/social_networking/socialnetworking/model/beans/catalogue/CatalogueEvent.java
+++ b/src/main/java/org/gcube/social_networking/socialnetworking/model/beans/catalogue/CatalogueEvent.java
@@ -39,7 +39,7 @@ public class CatalogueEvent {
 	 * the URL to redirect when clicking on the notification
 	 */
 	@JsonProperty("itemURL")
-	@NotNull(message="itemURL cannot be missing")
+	@NotNull(message="itemURL cannot be missing, use catalogue resolver URL")
 	protected URL itemURL;
 
 	/**