Why is telethon showing an error when trying to get users from a telegram group? – Telegram API

I am trying to get users from a group using a telegram bot . I am using python’s telethon library for this purpose . Here is the code and the full error message –

from telethon import TelegramClient, events
API_ID = 123
API_HASH = '##'  
BOT_TOKEN  ="##" 
bot = TelegramClient('bot', API_ID, API_HASH)
bot.start(bot_token=BOT_TOKEN) 
async def Get_Random():
    users = await bot.get_participants(-123)
    print(users[0].first_name)
    for user in users:
        if user.username is not None:
            print(user.username)
bot.loop.run_until_complete(Get_Random())

Full error –

telethon.errors.rpcerrorlist.PeerIdInvalidError: An invalid Peer was used. Make sure to pass the right peer type and that the value is valid (for instance, bots cannot start conversations) (caused by GetFullChatRequest)

Bot is already an admin of the group .