Restrict Paypal to accept only payments from USA customers only

Question

I am using Adaptive Payment and I want to pay re-seller after cut down my commission:

I want to charge different rates for domestic (USA) transactions versus foreign transactions.

Domestic: 3.0% + $0.30 per transaction

PayPal: 2.9% + $0.30 per transaction

Net gain: +0.1%

Foreign: 4.0% + $0.30 per transaction

PayPal: 3.9% + $0.30 per transaction

Net gain: +0.1%

Since rates are different so I have planned to allow only USA customer to pay. but I do not know where the credit card is from or what rate PayPal is going to charge.

Moreover, here is the code that we are using to sent request and do not find any parameter to restrict it to domestic payments.

@api = PayPal::SDK::AdaptivePayments::API.new
            @pay = @api.build_pay({
              :item_name => 'Invoiced #'+invoice.id.to_s+invoice.reason,
              :invoice_amount => amount['total_amount'],
              :actionType => "PAY",
              :cancelUrl => pay_finish_members_invoices_url(:id=>token,:ttn_id=>ttn_token,:status=>"Cancel"),
              :currencyCode => "USD",
              :feesPayer => "PRIMARYRECEIVER",
              :ipnNotificationUrl => pay_finish_members_invoices_url(:id=>token,:ttn_id=>ttn_token,:status=>"Completed"),
              :trackingId => tmp_transaction.id.to_s,
              :memo => "Single invoice paid by member directly.",
              :receiverList => {
                :receiver => [
                    { :amount => amount['total_amount'],
                      :email => Trunk::PAYPAL_EMAIL,
                      :primary => true,
                      :paymentType => "SERVICE"
                    },
                    { :amount =>  amount['coach_amount'],
                      :email => @site_settings.paypal_email,
                      :primary => false,
                      :paymentType => "SERVICE"
                     }
                ]
              },
              :returnUrl => pay_finish_members_invoices_url(:id=>token,:ttn_id=>ttn_token,:status=>"Completed"),
=begin
              :fundingConstraint => {
                :allowedFundingType => {
                  :fundingTypeInfo => [{
                    :fundingType => "BALANCE" }] } 
              },
=end
              :sender => {
                :useCredentials => false
               }
            })


            @pay_response = @api.pay(@pay)
            #abort(@pay_response.inspect)

            if @pay_response.success?
              @pay_response.payKey
              @pay_response.paymentExecStatus
              @pay_response.payErrorList
              @pay_response.paymentInfoList
              @pay_response.sender
              @pay_response.defaultFundingPlan
              @pay_response.warningDataList
              params = {
                :cmd => "_ap-payment",
                :paykey =>  @pay_response.payKey
              }
              paypal_url = "#{Trunk::PAYPAL_URL}?#{params.to_query}"
              tmp_transaction = TempTransaction.where(:id => tmp_transaction.id).first
              tmp_transaction.txn_id = @pay_response.payKey
              tmp_transaction.status = 1
              tmp_transaction.save
              redirect_to paypal_url and return
            else
              flash[:alert] = @pay_response.error.to_s
            end