This article has instructions on how to invite external contacts to Skype for Business Meetings.
Note: In order to be able to invite external contacts, you need to create SRV record for your domain name. Read Knowledge Base article How To Fix External Contact's Sign-in To Lync Attendee for more information.
- Make sure that Skype for Business Secure Chat and Conferencing service is installed on the account, enabled for the user and the Skype for Business client is downloaded and set up. Read the Knowledge Base articles on Getting Started With Skype for Business For Windows or Getting Started With Lync 2010/2013 For Windows or Getting Started With Lync For Mac.
- Sign in to Skype for Business on the Desktop. Click on Meet Now in the drop down menu.
- Select Use Skype for Business on Join Meeting Audio and click OK.
- Click More Options and select Meeting Entry Info.
- Copy the link and send it to the desired contact.
Important: This invitation link will resolve to Server Error: 404 File or Directory not found if the Lync Secure Chat and Conferencing service is installed on the account less than 24 hours ago. The maintenance tasks need to be performed first, in the maintenance windows (3-5 am PST).