I had created a RSV for practice and had a VM and file storage as backup items. Later I deleted the backup items and the VM and storage resource. Yet when i delete the vault i get this error about an existing resource which in fact does not exist.
There are no backup items for the vault
There are no backup jobs, policies , literally anything attached to the VM
The resource group has nothing except the vault
I have deleted everything possible and yet I am not able to delete the vault itself




In my environment, I encountered the same error:
To delete the Recovery Service Vault, first, you need to unregister your storage account from the Recovery Service Vault.
To unregister, Go to Portal -> Your Recovery Service Vault -> Backup Infrastructure -> Storage Accounts -> Unregister.
Portal:
After unregistering the storage accounts, I was able to delete my Recovery Service Vault.
Portal: