TypeError: bot.sendMessage is not a function

[BrunoMonteiro92]

After running it, when I write liftoff, it gives me this error:

bot.sendMessage(authorChannel, text);
      ^

TypeError: bot.sendMessage is not a function
    at sendMessage (C:\Users\-Bruno\Documents\GitHub\Samplebot\index.js:70:7)
    at C:\Users\-Bruno\Documents\GitHub\Samplebot\index.js:169:11
    at Map.forEach (native)
    at Client.<anonymous> (C:\Users\-Bruno\Documents\GitHub\Samplebot\index.js:159:14)
    at emitOne (events.js:96:13)
    at Client.emit (events.js:188:7)
    at MessageCreateHandler.handle (C:\Users\-Bruno\node_modules\discord.js\src\client\websocket\packets\handlers\MessageCreate.js:9:34)
    at WebSocketPacketManager.handle (C:\Users\-Bruno\node_modules\discord.js\src\client\websocket\packets\WebSocketPacketManager.js:103:65)
    at WebSocketConnection.onPacket (C:\Users\-Bruno\node_modules\discord.js\src\client\websocket\WebSocketConnection.js:330:35)
    at WebSocketConnection.onMessage (C:\Users\-Bruno\node_modules\discord.js\src\client\websocket\WebSocketConnection.js:293:17)