'variable' is not captured

QVector<QTcpSocket *> readers;
 
void MyTcpServer::slotNewConnection()
{
    newClientSocket = mTcpServer->nextPendingConnection();
 
    newClientSocket->waitForReadyRead();
 
    QByteArray Message = newClientSocket->readAll();
 
    qDebug() << Message;
 
    if (Message.contains("Sender"))
    {
        senders.push_back(newClientSocket);
 
        int ClientNumber = senders.size() - 1;
 
        connect(senders.at(ClientNumber), &QTcpSocket::readyRead, [this](){this->slotClientRead(ClientNumber);});
        connect(senders.at(ClientNumber), &QTcpSocket::disconnected, [this](){this->slotClientDisconnected(ClientNumber);});
    }
 
}

        connect(senders.at(ClientNumber), &QTcpSocket::readyRead, [this, ClientNumber](){this->slotClientRead(ClientNumber);});
        connect(senders.at(ClientNumber), &QTcpSocket::disconnected, [this, ClientNumber](){this->slotClientDisconnected(ClientNumber);});

senders.push_back(newClientSocket);
 
int ClientNumber = senders.size() - 1;
 
connect(senders.at(ClientNumber), &QTcpSocket::readyRead, [this](){this->slotClientRead(ClientNumber);});
connect(senders.at(ClientNumber), &QTcpSocket::disconnected, [this](){this->slotClientDisconnected(ClientNumber);});

connect(newClientSocket, &QTcpSocket::readyRead, [this](){this->slotClientRead(senders.size() - 1);});
connect(newClientSocket, &QTcpSocket::disconnected, [this](){this->slotClientDisconnected(senders.size() - 1);});
senders.push_back(newClientSocket);