Assume that you create an online meeting as a presenter in Microsoft Lync 2013 (Microsoft Skype for Business), and then you share the meeting URL. The present button isn't displayed in your conversation window when one of the following conditions is true:
When the first user opens the URL, and then selects the Call Me At option to join the meeting from Lync (Skype for Business) Web App as a guest.
Note When another user joins the meeting as a guest, the button is displayed again.
When the first user dials in to the meeting as a guest.
Note All users have the presenter permission. However, the present button is visible for the guest users.
To fix this issue, install the March 8, 2016 update (KB3114831) for Lync 2013 (Skype for Business).
Note Lync 2013 was upgraded to Skype for Business in April 2015.