It looks like DriveThruRPG have removed their publisher RSS feeds some time in the last few weeks. We have reached out to them to inquire about it, but aside from confirmation that these feeds no longer work, we do not know anything else about it yet.
Unfortunately, this means the import from DriveThruRPG to RPG Trader isn’t possible anymore, so we have removed it from the bulk import page. We have also updated the documentation to indicate that it is no longer possible.
This is a great pity, and entirely out of our control. If an import becomes possible again in the future, we’ll make sure to implement it. In the meantime, the CSV and Itch imports still work as expected.