Is it possible to transfer a chat bot from one constructor to another while maintaining subscribers?

Question

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Interested in each messenger separately: Telegram, Viber, VK and Facebook Messenger
I heard that it is impossible to do this and subscribers will not be saved

Answer 1

I'll tell you about Telegram (if something is inaccurate, I hope they will correct me):
A "subscriber" of a bot is a user who allowed the bot to write to himself (via the "/start" command).
On Telegram servers, information about which user is subscribed to which bots is indeed stored somewhere. However, this information is not available to bot owners, and there is no easy way for a bot to get a list of its subscribers (iterating through all telegram users is not an easy way). Also, bots do not have a way to see their "sent" messages + ways to receive "incoming" de facto do not allow viewing the history of "incoming" from the server more than 2 days ago. Thus, there is no way to get a list of subscribers from the Telegram server.
Bot owners solve the problem of monitoring the list of subscribers and correspondence by keeping all correspondence histories and statuses themselves. In your case, all this information is stored in the constructor/server on which the bot itself runs. Thus, it is possible to transfer subscribers if you somehow unload the list of subscribers or the history of correspondence from one constructor (if he himself stores it) and upload it to another.
UPD: This was all described for the case when the bot account remains the same, but the servers / constructor change. If the bot account in Telegram changes, then even uploading the list of subscribers will not help. In Telegram, a bot cannot write to a person who has not subscribed to this bot. The only way to convert subscribers is through the old account / constructor (or from the account of some person, but this will already be spam) to ask users to switch to a new bot account.