Merge pull request #5421 from segmentio/bobbyatsegment-patch-7

Add section on Set Once/Set Always fields

Author: rchinn1

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

@@ -214,7 +214,15 @@ Keep the following in mind if you plan to move to Amplitude (Actions) from a cla
 You configure the Amplitude (Actions) destination through Filters and Actions. Consult the table below for information about configuring your Amplitude (Actions) destination similarly to your classic Amplitude destination.
 
 > info ""
-> Contact Segment support if you find features missing from the Amplitude (Actions) destination that were available in the classic Amplitude destination.
+> Contact Segment support if you find features missing from the Amplitude (Actions) destination that were available in the classic Amplitude destination. 
+
+### Set Once/Set Always fields
+
+Amplitude restricts the mixing of top-level user properties with `$set`, `$setOnce`, or `$setAlways` operations in a single request, [as outlined in Amplitude’s documentation](https://www.docs.developers.amplitude.com/analytics/apis/identify-api/#user_properties-supported-operations){:target="_blank"}. 
+
+To circumvent this within Segment, users can opt to exclusively map event parameters to either the **User Properties** field or to one of the user property operations (Set Once and/or Set Always) available in mappings. If you use the **Set Once** and/or **Set Always** fields, include all relevant fields in their respective mappings and do not configure mappings for **User Properties** in the same request.
+
+Conversely, to send top-level user properties, map only to the **User Properties** field and exclude mappings for the **Set Once** and **Set Always** fields. 
 
 {% include components/actions-map-table.html name="amplitude" %}