I have sent Request: 

----------------------------------

{
"id":"1",
"intent":"sale",
"payer":{
"payment_method":"credit_card",
"funding_instruments":[
{
"credit_card_token":{
"credit_card_id":"CARD-52935783CV043764NLLKG66Q",
"external_customer_id":"608"
}
}
]
},
"transactions":[
{
"amount":{
"total":"6.70",
"currency":"USD"
},
"description":"Payment by vaulted credit card."
}
]
}

-----------------------

i got response 

{
"name": "INTERNAL_SERVICE_ERROR",
"message": "An internal service error occurred.",
"information_link": "https://developer.paypal.com/docs/api/payments/#errors",
"debug_id": "78913847a0d24"
}

Plz advise