Question

Why doesn't the button display below the message? 

  await message.answer (f "Hello {message.from_user.first_name}!",
                         reply_markup = InlineKeyboardMarkup (InlineKeyboardButton ('callback', callback_data = 'callback')))

Answer 1

You can make use of the given below given:

reply_markup=InlineKeyboardMarkup().add(InlineKeyboardButton(text='callback', callback_data='callback'))