If you have sufficient access (see General Data Source Access Requirements) to a Facebook ad account but it is not appearing in the account drop-down in Supermetrics tools, kindly check that you have not been granted access to the ad account through a 'Business Asset Group' as Ad Accounts whose permissions have been granted through an asset group may not show up in the account selection window within the Supermetrics connector.
Solution: ask your organisation admin to assign you directly to the Ad Account.
I've now been assigned directly to the ad account but it still doesn't show up in the Supermetrics connector!
Please follow the steps in this guide then: