Telegram bot keybord send via JSON

I'm using MS Bot Framework. I want to sen custom keyboard to user, so i try to reply message with this JSON:

                replyMessage.ChaelData = @"
{
    ""method"": ""sendMessage"",
    ""parameters"":
    {
        ""reply_markup"":
        {
            ""keyboard"":[[""1"",""2""],[""3""],[""4"",""5"",""6""]],""one_time_keyboard"":true
        }
    }
}

";

But nothing happens. For example, this message with sticker works fine:

                replyMessage.ChaelData = @"
{
    ""method"": ""sendSticker"",
    ""parameters"":
    {
        ""sticker"":
        {
            ""url"": ""https://upload.wikimedia.org/wikipedia/commons/3/33/LittleCarron.gif"",
            ""mediaType"": ""image/gif""
        }
    }
}

";

I think that the problem is in "keyboard" part, somewhere in array.