Late but...
- Go to "Careers"
- Scroll to the Dragon Age Inquisition tab (via clicking the "triangle" at the top left just below Career which will show a drop down menu)
- Cycle to "Rewards" on Page 6 via clicking the arrow to the right
- Select "Completed The Last Court"
- Find the "unlock" button somewhere on the pop up
- Voila~! You have successfully "done" it and it should allow you to do the Serrault Glass War Table Mission ;3
PS: You can do it for most everything else too... Even the "Premium" DLCs (item packs) that were once "paid" can be gotten for free this way by going to the DLC section and "unlocking" it with a simple click.
Hope this helps.
.png){kind=link}