sendMessage with "message_thread_id=1" returns "BadRequest: Message thread not found"

[gerkatheking]

this is the original report from another person
python-telegram-bot/python-telegram-bot#4739 (comment)

it is impossible to "reply in another chat" using sendMessage when destination is general topic of the chat.
if you set message_thread_id 1 => 400 message thread not found
if you don't specify message_thread_id it replies in the source thread of reply_to_message_id message.

[levlam]

Does the forum chat have more than 1 million messages?

[gerkatheking]

No, It reproduces in empty chat.

[levlam]

Are you sure that the chat is a forum chat?

[gerkatheking]

yes and sendMessage response has "is_forum": true

[foremtehan]

I have a forum chat with millions of messages and i can confirm the bot could not send message to some of them and i'm wondering why i'll recieve thread not found?

[levlam]

Can you reproduce the issue in Bot API 9.3?
If so, could you send the full request as a link to api.telegram.org to https://t.me/tdlib_bot?