Artifact Signing: certificate profile creation fails with ResourceCreationValidateFailed (x-ms-failure-cause: service)

I cannot create ANY certificate profile in my Trusted Signing (Artifact Signing) account. Every attempt fails with HTTP 400 "ResourceCreationValidateFailed / The resource validation failed", and the response header shows x-ms-failure-cause: service (a service-side failure, not a client/payload issue).

Verified prerequisites (all correct):

• Subscription is PayAsYouGo, state Enabled, spending limit Off.
• Resource provider Microsoft.CodeSigning is Registered.
• Code signing account provisioningState = Succeeded.
• Organization identity validation is Completed/Approved.

The failure is identical for:

• profileType PublicTrust (with a valid identityValidationId provided)
• profileType PublicTrustTest
• API versions 2025-10-13 (GA) and 2026-05-15-preview
• Both the Azure portal and direct ARM REST PUT calls.

Account region: West Europe (westeurope), SKU Basic.

x-ms-failure-cause is "service" and all client-side prerequisites are verified. Please have the Artifact Signing engineering team review the backend logs. I can privately provide the Subscription ID, Tenant ID, account name, identity validation ID, and the failed-request correlation IDs on request.