针对此问题，可以在客户端实现一个对未收到服务器响应的队列进行管理的逻辑，当接收到一条新的交易时，将其加入队列中，并设置一个超时时间。当超时时间到达时，如果服务器还未响应，则可以将该条交易重新发送至服务器。同时，在服务器端可以增加一个对于重复交易 ID 的判断逻辑，当检测到重复交易 ID 时，可以直接返回该交易已经处理成功的响应，避免重复处理。以下是 Swift 实现代码示例：

客户端：

class PaymentQueue {
    var transactions: [Transaction] = []
    
    func addTransaction(_ transaction: Transaction) {
        transactions.append(transaction)
        DispatchQueue.main.asyncAfter(deadline: .now() + 30) { [weak self] in
            if let index = self?.transactions.firstIndex(where: { $0.id == transaction.id }) {
                self?.transactions.remove(at: index)
                self?.addTransaction(transaction)
            }
        }
    }
    
    func removeTransaction(_ transaction: Transaction) {
        if let index = transactions.firstIndex(where: { $0.id == transaction.id }) {
            transactions.remove(at: index)
        }
    }
}

struct Transaction {
    let id: String
    let amount: Double
}

服务器端：

app.post('/receivePayment', (req, res) => {
    const transactionId = req.body.transactionId;
    if (isDuplicateTransaction(transactionId)) {
        res.json({ success: true });
        return;
    }
    saveTransactionToDatabase(transactionId);
    processTransaction(transactionId);
    res.json({ success: true });
});

function isDuplicateTransaction(transactionId) {
    // Check if the transactionId is already processed before
}

function saveTransactionToDatabase(transactionId) {
    // Save the transaction to the database
}

function processTransaction(transactionId) {
    // Process the transaction
}