Unable to create App Service Plan for Function App — ServerFarmCreationNotAllowed

Hello,

I’m trying to deploy a FortiGate Autoscale solution that includes an Azure Function App created via ARM (nested deployment: CreateFunctionApp). The deployment consistently fails with:

The subscription '<SUBSCRIPTION_ID>' is not allowed to create or update the serverfarm.
Code: ServerFarmCreationNotAllowed

Context

Subscription recently upgraded from Free Trial to Pay-As-You-Go (Azure Plan).

Role: Owner on the subscription.

Resource providers Microsoft.Web, Microsoft.Insights, and Microsoft.OperationalInsights are Registered.

No Azure Policy assignments blocking Microsoft.Web.

Regions tested: East US and Australia Central.

The Fortinet template only exposes Service Plan Tier = Premium (P1v2) or Free (for demo only). Choosing either results in the error above during template validation.

Important observation

I can create a Function App manually in Consumption (Y1) or Flex Consumption via the portal, so permissions appear fine. The error only occurs when the template attempts to create Microsoft.Web/serverfarms (App Service Plan).

Request

• Please enable/allow creation of App Service Plans for this subscription so ARM can create a Function App in Consumption (Y1) (or advise which tiers are allowed and how to make the ARM validation pass).
• If there is any backend restriction left from the Free Trial → PAYG upgrade, please remove/unlock it.