If you are unable to connect your Instagram or Facebook account with Roster and you are getting an error message related to your "Off-Facebook" activity being turned off, the following information will be helpful for you to get it turned back on so you can connect your account with other apps like Roster.
This explains what "Off-Facebook" activity is:
This explains how you may have disconnected your "Off-Facebook" activity in the past:
Follow this link to your Facebook account to enable "Off-Facebook Activity" by clicking on "Manage Future Activity" and then go back into the Roster app and connect your social account.
Here's an example of the error message you may be hitting: