Hi,
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After you buy an Azure Reserved Virtual Machine Instance, the reservation discount is automatically applied to virtual
machines that match the attributes and quantity of the reservation. A reservation covers the compute costs of your virtual machines.
The Azure reservation discount is applied to running VM instances on an hourly basis. The reservations that you have purchased are matched to the usage emitted by the running VMs to apply the reservation discount.
No problem if you created the vm after the reservation,
it works just like this, after you create the reservation and create the vm of that sku the reservation is automatically applied
ref link:
Hope this helps
Cheers
Luca
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