Update migration-api-whats-new.md

Added new feature to the what's new topic, regarding job postponement and the correcsponding code.

Author: JoanneHendrickson

docs/apis/migration-api-whats-new.md

@@ -1,7 +1,7 @@
 ---
 title: "Migration API What's new"
 description: "Learn about the new features and updates to the Migration API."
-ms.date: 04/10/2023
+ms.date: 08/21/2023
 ms.reviewer: jhendr
 author: JoanneHendrickson
 ms.author: jhendr
@@ -16,6 +16,20 @@ ms.custom: admindeeplinkSPO
 
 Check here to see what features or updates have been added to the Migration API. Here's a summary of what's included.
 
+## Updated reason code and descriptions
+
+We have updated Migration API to provide detailed reasons in case a job is postponed. We encourage ISVs take appropriate actions, based on the reasons.
+
+|Possible reasons |Code|Description|
+|:-----|:-----|:-----|
+|DB busy|1，2，3，4|Target DB is busy, the job will be picked up again later|
+|VM busy |5，6|VM is busy, the job will be picked up again later|
+|DB defragment |7|Target DB is doing index defragment, please wait|
+|Tenant blocked |10|Target tenant is blocked from doing migration|
+|Other|11|Unknown reason|
+|Backend not ready yet |12|Backend is not ready yet, please wait|
+
+
 ## New: Speed up small file migration
 
 The migration package includes multiple files, which are each uploaded/downloaded individually. If you have a large number of small-sized files, migration speed drops dramatically. By using the new **ArchivedFiles.XML** file in your prime package you can transfer files in batch resulting in a faster migration. [Learn more about using the ArchivedFiles.XML](/sharepoint/dev/apis/migration-api-overview#archivedfilessxml)