A sales channel can only be connected to one Link My Books account at a time (you can have multiple additional users with access to it, but it can only be connected once).
Therefore if you try to connect up a channel which is already connected on Link My Books, this won’t complete and you'll receive an error message like this:
Often this can happen if you log in with a different email address login than the one you set up Link My Books with, and then try connecting the channel again after not seeing your channel connected as expected. Please log in with your original email login to view your account already connected.
Or perhaps you have already set up your Link My Books account but now want your accountant to have your sales channel on their account and so are trying to connect up again under their invitation, or vice versa. Please contact the support team so that we can migrate your account over for you.
There may be another reason you are trying to connect up again. Please contact support for assistance, providing further detail and the reference number given in the ‘duplicate account’ error message.