Unfortunately, it is not possible to recover a message which is permanently deleted from facebook messenger app. But if you have archived the conversation instead of deleting it, you can easily retrieve it from the option of archive chats. Plus if you have notification or email enabled you may find some part of conversation in email. First you have to log in to facebook and then visit setting and privacy. then setting and choose your facebook information. then click on download your information and then messages

Source: https://guideet.com/how-to-recover-deleted-messages-on-messenger/

If you have accidentally deleted messages on Facebook Messenger, there is some possibility of recovering them.

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