核心代码：

引入头文件：#import <StoreKit/StoreKit.h>
代理：SKProductsRequestDelegate,SKPaymentTransactionObserver
设置支付服务：[[SKPaymentQueue defaultQueue] addTransactionObserver:self]
结束时销毁：[[SKPaymentQueue defaultQueue] removeTransactionObserver:self];

1、初始化SKProductsRequest请求

// 初始化请求
SKProductsRequest *productsRequest = [[SKProductsRequest alloc]initWithProductIdentifiers:productSet];
 self.request = productsRequest;
// 设置delegate
productsRequest.delegate = self;
 // 开始请求
 [productsRequest start];

2、在代理的方法中处理业务逻辑

#pragma mark -- SKProductsRequestDelegate <收到返回的信息>
- (void)productsRequest:(nonnull SKProductsRequest *)request didReceiveResponse:(nonnull SKProductsResponse *)response {
   // 发送购买请求，创建票据，这个时候就会有弹窗了
    SKPayment *payment = [SKPayment paymentWithProduct:requestProduct];
    // 将票据加入到交易队列
    [[SKPaymentQueue defaultQueue] addPayment:payment];
}

#pragma mark -- SKPaymentTransactionObserver <监听购买结果>
- (void)paymentQueue:(nonnull SKPaymentQueue *)queue updatedTransactions:(nonnull NSArray<SKPaymentTransaction *> *)transactions {
    for (SKPaymentTransaction *transaction in transactions) {
        switch (transaction.transactionState) {
            case SKPaymentTransactionStatePurchased:
                // 请求服务器，验证购买
                [[SKPaymentQueue defaultQueue] finishTransaction:transaction];
                break;
            case SKPaymentTransactionStateRestored:
                // 恢复商品，已经购买过商品
                [[SKPaymentQueue defaultQueue] finishTransaction:transaction];
                break;
        
            case SKPaymentTransactionStateFailed:
                // 购买商品失败
                [[SKPaymentQueue defaultQueue] finishTransaction:transaction];
                break;
                
            case SKPaymentTransactionStatePurchasing:
                // 正在交易
                break;
                
            default:
                break;
        }
    }
}