Microsoft Graph rich subscription creation fails for GCC clients.

 I’m trying to create a Microsoft Graph subscription to watch Outlook events with encrypted resource data. My request body looks like this:

{
    "changeType":"updated,deleted",
    "notificationUrl":"https://my-inbound.url",
    "lifecycleNotificationUrl":"https://my-inbound.url",
    "resource":"users/<redacted>/events?$select=id,subject,start,end,attendees,isCancelled,isOrganizer,iCalUId,uid,bodyPreview,uid,organizer,onlineMeeting,onlineMeetingUrl,changeKey,sensitivity,lastModifiedDateTime,originalEndTimeZone,createdDateTime,allowNewTimeProposals,hasAttachments,singleValueExtendedProperties",
    "expirationDateTime":"2025-08-15T12:02:19.124967+00:00",
    "includeResourceData":true,
    "clientState":"<redacted>",
    "encryptionCertificate":"<redacted>",
    "encryptionCertificateId":"<redacted>"
}

When I POST to:

https://graph.microsoft.us/v1.0/subscriptions

I get the following error:

{
    "error": {
        "code": "ExtensionError",
        "message": "Operation: Create; Exception: [Status Code: BadRequest; Reason: were unable to deserialize ]",
        "innerError": {
            "date": "2025-08-13T12:18:05",
            "request-id": "cde172db-4cc2-4cd2-9e1c-63f46f36d0e3",
            "client-request-id": "cde172db-4cc2-4cd2-9e1c-63f46f36d0e3"
        }
    }
}

This request payload works for all our clients except those on Microsoft GCC High. Is there a different setup required when configuring clients in GCC High?