以下是生成支付的代码片段，伪代码

function createPayPal(){
 $shippingPrice = 2;
 $taxPrice = 0;
 $subTotal = 26;
 $item1 = new PayPalApiItem();
 $item1->setName("产品2")->setCurrency("USD")->setQuantity(1)->setPrice(10);
 $item2 = new PayPalApiItem();
 $item2->setName("产品1")->setCurrency("USD")->setQuantity(2)->setPrice(8);

 $itemList = new PayPalApiItemList();
 $itemList->addItems([$item1,$item2]);

 // Set payment details
 $details = new PayPalApiDetails();
 $details->setShipping($shippingPrice)->setTax($taxPrice)->setSubtotal($subTotal);

 // Set payment amount
 //注意，此处的subtotal，必须是产品数*产品价格，所有值必须是正确的，否则会报错
 $total = $shippingPrice + $subTotal + $taxPrice;
 $amount = new PayPalApiAmount();
 $amount->setCurrency("USD")->setTotal($total)->setDetails($details);

 // Set transaction object
 $transaction = new PayPalApiTransaction();
 $transaction->setAmount($amount)->setItemList($itemList)->setDescription("这是交易描述")
 ->setInvoiceNumber(uniqid());//setInvoiceNumber为支付唯一标识符,在使用时建议改成订单号

 $payer = new PayPalApiPayer();
 $payer->setPaymentMethod('paypal');//["credit_card", "paypal"]
 $redirectUrls = new PayPalApiRedirectUrls();
 $redirectUrl = "http://test.com/redirect/success";//支付成功跳转的回调
 $cancelUrl = "http://test.com/redirect/cancel";//取消支付的回调
 $redirectUrls->setReturnUrl($redirectUrl)->setCancelUrl($cancelUrl);

 // Create the full payment object
 $payment = new PayPalApiPayment();
 $payment->setIntent("sale")->setPayer($payer)->setRedirectUrls($redirectUrls)->addTransaction($transaction);

 try {
 $clientId = "xxxxxx";//上面应用的clientId和secret
 $secret = "XXXXXX";
 $oAuth = new PayPalAuthOAuthTokenCredential($clientId, $secret);
 $apiContext = new PayPalRestApiContext($oAuth);
 if(env('APP_DEBUG') === false ){
 $apiContext->setConfig(['mode' => 'live']);//设置线上环境,默认是sandbox
 }
 $payment->create($apiContext);
 $approvalUrl = $payment->getApprovalLink();
 dd($approvalUrl);//这个是请求支付的链接，在浏览器中请求此链接就会跳转到支付页面
 } catch (Exception $e) {
 dd($e->getMessage());//错误提示
 }
 }

以下是支付成功的回调代码片段，伪代码

function payRedirect(Request $request)
 {
 $paymentID = $request->get('paymentId');
 $payerId = $request->get('PayerID');

 $clientId = "xxxxxx";//上面应用的clientId和secret
 $secret = "XXXXXX";
 $oAuth = new PayPalAuthOAuthTokenCredential($clientId, $secret);
 $apiContext = new PayPalRestApiContext($oAuth); 
 if(env('APP_DEBUG') === false ){
 $apiContext->setConfig(['mode' => 'live']);//设置线上环境,默认是sandbox
 }
 $payment = PayPalApiPayment::get($paymentID, $apiContext);

 $execute = new PayPalApiPaymentExecution();
 $execute->setPayerId($payerId);

 try{
 $payment = $payment->execute($execute, $apiContext);//执行,从paypal获取支付结果
 $paymentState = $payment->getState();//Possible values: created, approved, failed.
 $invoiceNum = $payment->getTransactions()[0]->getInvoiceNumber();
 $payNum = $payment->getTransactions()[0]->getRelatedResources()[0]->getSale()->getId();//这是支付的流水单号，必须保存，在退款时会使用到
 $total = $payment->getTransactions()[0]->getRelatedResources()[0]->getSale()->getAmount()->getTotal();//支付总金额
 $transactionState = $payment->getTransactions()[0]->getRelatedResources()[0]->getSale()->getState();//Possible values: completed, partially_refunded, pending, refunded, denied.

 if($paymentState == 'approved' && $transactionState == 'completed'){
 //处理成功的逻辑，例如：判断支付金额与订单金额，更新订单状态等
 return "success";//返回成功标识
 }else{
 //paypal回调错误,paypal状态不正确
 return "error";//返回错误标识
 }
 }catch(Exception $e){
 dd($e->getMessage());
 }
 }

退款必须要有支付成功的流水单号

一个流水单号可以进行多次退款

退款成功之后，在账号的交易记录中不体现，测试时请登录测试账号自己记录一下余额的变化情况，以确定退款是否成功

商家账号会减少余额并增加手续费（手续费是之前付款多收的），用户账号会增加余额

function refundOrder()
 {
 try{
 $refundRequest = new PayPalApiRefundRequest();
 $amount = new PayPalApiAmount();
 $amount->setCurrency("USD")->setTotal(10);//退总金额
 $refundRequest->setAmount($amount);
 $refundRequest->setDescription("退款测试");
 $sale = new PayPalApiSale();
 $sale->setId("XXXXXXXXX");//支付单号,支付成功时保存的支付流水单号
 $clientId = "xxxxxx";//上面应用的clientId和secret
 $secret = "XXXXXX";
 $oAuth = new PayPalAuthOAuthTokenCredential($clientId, $secret);
 $apiContext = new PayPalRestApiContext($oAuth);
 if(env('APP_DEBUG') === false ){
 $apiContext->setConfig(['mode' => 'live']);//设置线上环境,默认是sandbox
 }
 $detailedRefund = $sale->refundSale($refundRequest, $apiContext);//调接口
 $refundState = $detailedRefund->getState();//Possible values: pending, completed, cancelled, failed.

 //var_dump($refundedSale);
 if($refundState == 'completed'){
 //退款成功,返回
 }else{
 dd('paypal 退款失败, 状态不正确');
 }
 }catch (Exception $exception){
 dd($exception->getMessage());//发生异常
 }
 }

更多接口代码示例

http://paypal.github.io/PayPal-PHP-SDK/sample/