We are managing our customers' azure subscriptions using Microsoft Partner Center >> and using a username I create a new Azure Vault for a customer>> but when I tried to create a new Secret inside the Azure Vault , I got this error:-
The operation "Set" is not enabled in this key vault's access policy.

now when I access the Key Vault >> Access Policy >> I am unable to add the login username which I used to create the Key Vault inside the Key Vault access policy, where I am only able to add the office 365 admin:-

so any advice why i am able to create a new Key Vault, while i am unable to add Secrets inside it?