Merge pull request #2460 from segmentio/ga4-more-notes

Add more to GA4 docs

Author: pwseg

src/connections/destinations/catalog/actions-google-analytics-4/index.md

@@ -40,20 +40,30 @@ To add the Google Analytics 4 destination:
 
 {% include components/actions-fields.html %}
 
-## Troubleshooting
+## FAQ & Troubleshooting
 
 ### Custom Event Naming
 
 Google Analytics 4 does not accept custom event names that include spaces. Segment replaces spaces in the Event Name in the Custom Event action with an underscore. As a result, you will see custom events snakecased in Google Analytics 4.
 
 Google Analytics 4 is also case sensitive. If you would like all event names lowercased, use the `Lowercase Event Name` setting in the Custom Event action. If this setting is disabled, Google will treat event names with different casing as distinct events. For more information, see [Google Analytics 4 Event name rules](https://support.google.com/analytics/answer/10085872?hl=en&ref_topic=9756175#event-name-rules&zippy=%2Cin-this-article.%2Cin-this-article){:target="_blank"}.
 
+### Custom Dimensions & Metrics
+
+With Google Analytics 4, you must create custom dimensions and metrics within the Google Analytics 4 interface and link event parameters to the corresponding dimension or metric. When creating the dimension or metric, you can either select a parameter from the list of already collected fields or enter the name of the parameter you plan to collect in the future. For more information, see [Google Analytics 4 Custom dimensions and metrics](https://support.google.com/analytics/answer/10075209?hl=en)  
+
+### Debug Mode
+
+The Google Analytics 4 [debug mode](https://support.google.com/analytics/answer/7201382?hl=en){:target="_blank"} only works with a client-side implementation through gtag.js, Google Tag Manager, or Firebase. Because Segment’s Google Analytics 4 integration is server-side and uses the Measurement Protocol API, debug mode is not supported.
+
+### Mobile Data
+
+The Google Analytics 4 Measurement Protocol API is only compatible with web streams. Google requires use of their Firebase SDKs to send mobile data to Google Analytics 4. For more information on linking Google Analytics 4 properties to Firebase, see [Google Analytics 4 Firebase integration](https://support.google.com/analytics/answer/9289234?hl=en){:target="_blank"}.
+
 ### User Metrics & Sessions
 
 Segment sends a Google `clientId` in requests to the Measurement Protocol API, alongside other required API fields. However, user sessions are [not currently supported by the Measurement Protocol API](https://developers.google.com/analytics/devguides/collection/protocol/ga4/reference/limitations){:target="_blank"}, so user metrics might not appear on the Google Analytics 4 Realtime report or several other reports. 
 
 To validate your implementation, check users and events on the Events report and User Explorer.
 
-### Debug Mode
 
-The Google Analytics 4 [debug mode](https://support.google.com/analytics/answer/7201382?hl=en){:target="_blank"} only works with a client-side implementation through gtag.js, Google Tag Manager, or Firebase. Because Segment’s Google Analytics 4 integration is server-side and uses the Measurement Protocol API, debug mode is not supported.