Update migration-api-overview.md

Added paragraph to the ExportSettings section to detail the new requirement of SourceType, also added example.  Updated ms.date.

Author: JoanneHendrickson

docs/apis/migration-api-overview.md

@@ -311,6 +311,39 @@ The **ExportSettings.XML** file is expected to be at the root of the Azure Blob
 
 The main requirement is that the ExportSettings `SiteUrl` value must be populated with a URL consistent with the source URL used for the rest of the import package. In the case of file shares as a source, the URL would be pre-specified to be the source URL in the rest of the package, whereas a package generated through an export operation at a source site would be its original source site collection URL.
 
+#### SourceType required
+Beginning January 1, 2023, the SourceType field will be mandatory when calling the Migration API. Starting October 1st, 2022, a warning message will be sent if the field is missing.
+
+Accepted SourceType values:
+
+- AmazonS3
+- AzureStorage
+- Box
+- Dropbox
+- Egnyte
+- FileShare
+- GoogleCloudStorage
+- GoogleDrive
+- MicrosoftStream
+- OneDrive
+- SharePointOnline
+- SharePointOnPremServer
+- Other
+
+When declaring to **Other**, include *DetailedSource* to provide us the detailed information. 
+
+**Example**:
+
+```powershell
+
+<ExportSettings xmlns="urn:deployment-exportsettings-schema" SiteUrl="https://some site url" FileLocation="some paths" IncludeSecurity="All" SourceType="Other" DetailedSource="My special source type not in the list"> 
+  <ExportObjects> 
+    <DeploymentObject Id="GUID for list" Type="List" ParentId="GUID for web" /> 
+  </ExportObjects> 
+</ExportSettings> 
+
+```
+
 ### LookupListMap.XML
 
 The **LookupListMap.XML** file, if included, is expected to be at the root of the Azure Blob Store Container defined by the CreateMigrationJob’s azureContainerManifestUri parameter. This optional file is validated using the constrained **DeploymentLookupListMap.XSD**, which has no change from current published [full 2013 package schema](../schema/content-migration-schemas.md).