i want to to send private messages to all the mentioned users and also store the usernames in a vector. everything works, but the program just keeps on crashing on push_back(), it works in other places but just not inside this lambda. A begineer here, what implementation have i done wrong here?

std::vector<std::string> userNames;
for (int itr = 0; itr < message.mentions.size(); itr++)
{
    dpp::snowflake user_id_to_dm = message.mentions[itr].first.id;
        bot.direct_message_create(user_id_to_dm, dpp::message("Here's a private message!"),
        [event, &bot, message, &userNames, itr] (const dpp::confirmation_callback_t& callback)
        {
            if (callback.is_error())
            {
                bot.message_create(dpp::message(event.msg.channel_id,
                "I couldn't send a message to " + message.mentions[itr].first.username)
                .set_reference(message.id));
                return;
            }

        std::string nameTemp = message.mentions[itr].first.username;
        std::cout << "DM Sent to " << nameTemp << "n";
    userNames.push_back(nameTemp);
        });
}