I am getting the following error try to make sandbox credit card purchases when user has country set to US:

chargeOrder :: {"name":"INSTRUMENT_DECLINED","details":[],"message":"The instrument presented was either declined by the processor or bank, or it can't be used for this payment.","information_link":"https://developer.paypal.com/docs/api/payments/#errors","debug_id":"6472b22aae20d"}

Note, I do not get this error when using non-US user e.g. GB.