Hi Tom Leonard,
Thank you for reaching out to Microsoft Q&A forum
The error you are encountering is related to the regional vCPU quota in your Azure subscription. Although you are using a Pay-As-You-Go account, the quotas for certain VM families, such as the Standard_DDSv5 series, may be exhausted.
You can try deploying the AKS cluster in a different region where you have available regional vCPU quota. Alternatively, you can submit a request to increase the regional vCPU quota limit.
For further reference, please see the following document: Azure Regional Quota Requests.
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