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Based on the error screenshot shared, because the specified image is not available in the "East US" region, where your virtual machine scale set (VMSS) is located. However, the screenshot shared shows the Image and VMSS are in East US region only. That is weird.
Try to troubleshoot this by verifying the image and VMSS locations. Try VMSS update with another image to check the exact issue.
Confirm that the image you want to use for updating the VMSS is available in the "East US" region using the Azure CLI or PowerShell commands.
Ex for Azure CLI:
az vm image list --location eastus --publisher <publisher_name> --offer <offer_name> --sku <sku_name> --all
If the image is not available in the "East US" region, consider using an alternative image that is available in the same region.
Once you have confirmed that the desired image is available in the "East US" region, retrieve the correct
ImageReferenceId for that image. The
ImageReferenceId should be in the format:
Try to update VMSS with the correct image reference and see if that helps.
Hope that helps.