can't send message from bot to public channel

[mnabila]

i was try to send message from my bot to public channel with bot.sendMessage(chat_id="@ChannelName, text="some text") but I get an error message like this ('Bad Request: need administrator rights in the channel chat', 400, {'ok': False, 'error_code': 400, 'description': 'Bad Request: need administrator rights in the channel chat'})
how to fix it even though I have added the bot as an administrator on my channel ?
and below is the bot settings

thanks
sorry if my english bad

[IanBotashev]

Did you figure it out?

If not:
If i'm right, in the What can this admin do? field, Post messages is disabled, though for it to be able to send messages there it needs to be enabled for the bot.