@Mukesh Bhakar - Thank you for your post and I apologize for the delayed response!
What is the context where you are seeing this error? How are you attempting to deploy the blueprint? How are you confirming that you are an owner of the management group (MG)?
For what its worth, blueprints can only deploy resources to a single subscription at a time. If you want to apply a policy to all subs under a particular MG, that will require a blueprint assignment per sub. We allow you to store the blueprint assignment resource at an MG, but only to prevent a subscription owner from removing the blueprint assignment (and the lock associated with it). If the blueprint only has policies, then I’d recommend assigning the policy directly to the MG.
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