Static Web App cannot be deleted — orphaned linkedBackend is readable but returns 404 on DELETE/unlink

[Trent3759]

I have a Standard-tier Static Web App that cannot be deleted because of an orphaned linkedBackend record. The link points to a Web App that no longer exists, and the record is readable but unaddressable by the write/delete path. This has been blocking subscription cancellation for months.

Resource

• Subscription: <SUB_ID>
• Resource: /subscriptions/<SUB_ID>/resourceGroups/formflow-rg/providers/Microsoft.Web/staticSites/formflow-app-prod
• SKU: Standard, Region: eastus2
• Only resource in the subscription

Symptom

Both direct DELETE on the SWA and resource-group cascade DELETE fail with the opaque error:

{"code":"ResourceOperationFailure",
 "message":"The resource operation completed with terminal provisioning state 'Failed'.",
 "details":[{"code":"Unspecified","message":""}]}

Root cause visible from ARM

The site has a build named preview holding a linkedBackends record backend1 pointing at:

/subscriptions/<SUB_ID>/resourceGroups/formflow-rg/providers/Microsoft.Web/sites/formflow-backend-104793

That target Web App no longer exists (confirmed via az resource list across all my subscriptions). The link is dangling.

The metadata is in an inconsistent state:

• GET .../builds/preview/linkedBackends returns backend1 with provisioningState: Succeeded
• DELETE .../builds/preview/linkedBackends/backend1 → 404 NotFound on api-versions 2024-04-01, 2023-12-01, 2023-01-01, 2022-09-01, 2022-03-01, 2021-03-01
• POST .../linkedBackends/backend1/unlink and .../builds/preview/linkedBackends/backend1/unlink → 404 NotFound / BadRequest

So the record exists from the read path but is unaddressable from the write path. Only the platform can clear it.

Confirmation the linked backend is what's blocking everything

Attempting to downgrade the SKU to Free returns a clear error pointing at the same record:

Sku is invalid. Free SKU is invalid. Linked Backends are not allowed in this SKU.
The following builds have linked backends configured: preview

The downgrade path enumerates backend1 correctly; only the unlink/delete path cannot remove it. This is consistent with corruption in the linkedBackends storage on the RP side.

Activity-log entries

2026-04-28T13:56:11Z  Microsoft.Web/staticSites/linkedBackends/unlink/action         Failed/NotFound  → {"error":{"code":"BadRequest","message":""}}
2026-04-28T13:56:11Z  Microsoft.Web/staticSites/builds/linkedBackends/unlink/action  Failed/NotFound  → {"error":{"code":"BadRequest","message":""}}
2026-04-28T13:56:10Z  Microsoft.Web/staticSites/builds/linkedBackends/delete         Failed/NotFound  → "Resource Not Found"
2026-04-28T14:01:24Z  Microsoft.Web/staticSites/builds/delete                        Failed           → Unspecified

What I have tried

• DELETE on the Static Web App directly — Unspecified
• DELETE on resource group formflow-rg — Unspecified on staticSites/builds/delete
• DELETE on linkedBackends/backend1 across 6 API versions — all 404
• POST unlink action, both site- and build-scoped — 404 / BadRequest
• PATCH SKU Standard → Free — blocked by the dangling backend
• Subscription cancel via Microsoft.Subscription/cancel — blocked: ResourcesExistingOnSubscription
• Billing-API cancel via Microsoft.Billing/.../billingSubscriptions/.../cancel — not supported for Individual MCA
• DELETE builds/preview directly — accepted, but the cascading flow fails on the same record

Questions

1. Is there a supported way to force-remove a dangling linkedBackend whose target resource no longer exists, when both DELETE and the unlink action return 404 on the record itself?
2. If not, can someone from the Static Web Apps RP / Engineering team clear the backend1 record on build preview of formflow-app-prod server-side so the SWA can be deleted and the subscription closed?