I just installed k3b, but when I try to "Burn" I get an error: Please insert an empty or appendable DVD or Blu-ray medium

After opening k3b, I dragged a folder with about 1.3GB text files into a new data project. k3b seems to process the dragged folder OK, indicating a size of 1.3GiB but when I click "Burn" i get the above error.

There's a blank DVD in the drive. I've tried another blank disk as well with same results.
I can read disks from the drive with no issues.

I am running updated Fedora 33.

Can anyone help?

Thanks.
-Mike