It is is most likely because you dont have required permissions.
Ensure you have the Owner or Contributor role on subscription scope. Go to the Azure Portal > Subscriptions > Select the "Pay-As-You-Go" subscription > Access Control (IAM) > Check your role.
Also check that you do not have any policy restricting this.
- Navigate to Policy in the Azure Portal.
- View assignments for your subscription.
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Regards,
Abiola