You could also try this method Telegram Bot API
try sending reply mark up as null.
this worked for me
https://api.telegram.org/bot1234567-dddh4h4g3mrl-ilr5EfE/editMessageReplyMarkup?chat_id=-456777777082&message_id=1264&reply_markup={}
and removed key board.
the error you where getting, i believe was due to not having bot infront of botkey
and the delete works to
https://api.telegram.org/bot1234567-dddh4h4g3mrl-ilr5EfE/deleteMessage?chat_id=-456777777082&message_id=1264
which removes message and keyboard.
