In case you don't see comments on your dark (unpublished) posts synced in your Inbox, it could be for one of the following reasons:
You did not set up your ad account, yet. Here is what you need to do.
You have chosen the wrong ad account - sometimes, users use multiple ad accounts, so please double-check that you've selected the right ad account under which you run ads for that particular FB page.
There are no active ads - even if you select the correct ad account, there might be no active ads. We indicate this in ad account settings, please check if there is at least one active ad.
4. You have just set up your ad account recently - if you have just set up your account a few moments ago, don't worry, it takes an hour or two until we're able to sync all the necessary stuff and display comments on your dark posts. We recommend waiting 2 hours and then checking again.