where i received this request?
I have check everywhere 

@Dimedocs this message happens when there’s already a Manychat account connected to this IG account. The request is sent to the original Manychat account.

In this case you either have to track down who has connected that Manychat account so they can give you access to it, or you can talk to support to have them help you get access to the account (if there are no admins on that old account for whatever reason).

You can open a ticket at https://help.manychat.com 

Only the page owner can link manychat with instagram.