Help with Trakt to radarr sync?

Hi.
Just installed Flexget as a docker container and just starting to get it working, so total noob here.
I’ve got my config as below and trakt to sonarr seems to be working, but trackt to radarr doesn’t.

web_server: yes

schedules:
  - tasks: '*'
    interval:
      minutes: 1

tasks:
  trackt2sonarr:
    trakt_list:
      account: blah
      list: watchlist
      type: shows
    accept_all: yes
    list_add:
      - sonarr_list:
          base_url: http://docker.lan
          base_path: /sonarr
          port: 9105
          api_key: blahblahblahblahblahblahblah

  trackt2radarr:
    trakt_list:
      account: blahblah
      list: watchlist
      type: movies
    accept_all: yes
    list_add:
      - radarr_list:
          base_url: http://docker.lan/radarr
          port: 9104
          api_key: blahblahblahblahblahblahblah

One thing I’m thinking is that my radarr config uses a base url of /radarr - how do I specify that in the config? The radarr_list plugin doesn’t seem to take a base_path value.

The error I get is VERY (many pages) long:
2020-04-14 16:11:15 ERROR radarr trackt2radarr The movie add command raised exception: Invalid response received from Radarr: b'[\n {\n "title": "10 Cloverfield Lane",\n "alternative.....

Any ideas?

Thanks