How to make a simple bot for one-time use?

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Good afternoon.
There was a need for a bot, from which only 1 message is required per conversation, i.e. not so much a need for a bot as a message on behalf of the community.
I've already tried sending messages via the API, but with no success.
Does anyone have any ideas on how to quickly build a one-time bot with access to the conversation? Designers will also come if the chat function is in the free plan.