1. Upload your video to YouTube as Unlisted (you can select public if you don't mind the general public seeing the video; however Private videos do not work in Op Central)

  2. Ensure the "Allow Embedding" box is ticked (no others need to be - see reference image below). 
    If you need further guidance on privacy settings in YouTube, click here
  3. Open the uploaded video and copy the full URL from the address bar (not the embed code).

  4. Paste the link you've copied into the Reference URL field in Op Central. The video will appear with a playable thumbnail preview below.
    If you do not see the playable preview, then you have copy/pasted an incorrect link. 
    If you see a link that looks like this: https://youtu.be/______ it is an incorrect link.