NOT_ENABLED_TO_VAULT_PAYMENT_SOURCE error in some APIs / sandbox account

[Naraina]

I am encountering this 

{

    "name": "NOT_AUTHORIZED",

    "message": "Authorization failed due to insufficient permissions.",

    "debug_id": "f5432446befdb",

    "details": [

        {

            "issue": "NOT_ENABLED_TO_VAULT_PAYMENT_SOURCE",

            "description": "The API caller or the merchant on whose behalf the API call is initiated is not allowed to vault the given source. Please contact PayPal customer support for assistance."

        }

    ],

    "links": [

        {

            "href": "https://developer.paypal.com/docs/limited-release/payment-tokens/v3/api/#error-FORBIDDEN",

            "method": "GET"

        }

    ]

}

error in /v3/vault/setup-tokens API and /v2/scim/Users  in my sandbox account.
I want to save cards for future payments, and one more thing—correct me if I'm wrong—when creating setup tokens for cards, there's a customer parameter. However, as I explored PayPal, I noticed there are no APIs for creating customers except for ./v2/scim/Users 

[Naraina]

Also I noticed that my Vault feature is disabled in my sandbox account.