That means that you’re trying to connect the same Instagram account to another Manychat account, but that IG account is already connected to an old Manychat account. The request is sent to the Manychat account, not to the IG/FB account.
@Missviva Go to Meta Business Settings, and under the Users tab, click on Partners. Check if ManyChat is listed there; if it is, disconnect it and try again after 10 minutes.
That means that you’re trying to connect the same Instagram account to another Manychat account, but that IG account is already connected to an old Manychat account. The request is sent to the Manychat account, not to the IG/FB account.