One of the reasons you are not able to delete the “Recovery Services Vault” might an old storage account that was deleted but it is still linked to the vault.
The name of the storage account is actually listed in the error message.
To remove the associated account go to the vault and click on “Backup Infrastructure” in the “Manage” section.
Under “Storage Accounts” you can see the storage accounts associated with the vault.
Click “Unregister“…
Click “Delete“…
Wait for the account to be unregistered…
Once the account is unregistered successfully you should be able to remove the vault if no other resources are blocking it.