Add note about group by field (#2447)

* group by field

* change location

* Update configure-alerts.md

Updating text

_source/user-guide/alerts/configure-alerts.md

@@ -71,6 +71,9 @@ click **Preview** to open OpenSearch Dashboards in another tab. It can help revi
 
 ###### Group-by (order matters!)
 
+Alerts won't trigger if the field added to the Group-by doesn't exist in the logs. The logs must include both the field you have in group-by and the field you use in your query/filter to trigger the alert. 
+{:.info-box.important}
+
 You can apply **group by** operators to up to 3 fields. If you use this option, the alert will return the aggregated results.
 
 The order in which you add group-by fields matters. Results are grouped in the order in which the group-by fields are added. (The fields are shown from first to last from Left-To-Right.)
@@ -93,8 +96,6 @@ You’ll be able to use these fields to create the following chart:
 
 ![Alerts to visualization](https://dytvr9ot2sszz.cloudfront.net/logz-docs/correlated-alerts/group-by-visualize.png)
 
-
-
 ###### Accounts to search
 
 Next, select the **Accounts to search**. <!--An account is the equivalent of an Elasticsearch index.-->
@@ -213,4 +214,4 @@ The URL will look like this:
 
 `https://app.logz.io/#/dashboard/alerts/v2019/<<ALERT_ID>>`
 
-![Alert ID](https://dytvr9ot2sszz.cloudfront.net/logz-docs/alerts/alert-id.png)
+![Alert ID](https://dytvr9ot2sszz.cloudfront.net/logz-docs/alerts/alert-id.png)