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Hope you are trying to deploy VM in the available region and your subscription have enough Quota.
The N-Series VM's are not available in all the regions. Please check this link to see the availability in the region you are trying to deploy.
Check the available quota of these SKU's in your subscription. You need to request a limit increase based on your requirement. Refer below screenshot:
If you have enough quota for the specific SKU and you are trying to deploy VM in a supported region and you see the VM SKU is not available, then it could be a temporary capacity issue in that region. Request you to try in another region.
Hope this helps.
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