channel join request handler

handler.py

import asyncio
from aiogram import Bot, Dispatcher, types

bot = Bot(token='TOKEN')
dp = Dispatcher(bot)

@dp.chat_join_request_handler()
async def handle_chat_join_request(chat_join_request: types.chat_join_request.ChatJoinRequest):
    user_id = chat_join_request.from_user.id
    channel_id = chat_join_request.chat.id

    await bot.approve_chat_join_request(channel_id, user_id)

    await bot.send_message(user_id, 'Welcome to the channel!')

if __name__ == '__main__':
    print('Starting bot...')
    asyncio.run(dp.start_polling())