Hi, I believe I have found the issue, When I run the command in docker console "curl https://api.themoviedb.org/3/movie/popular?api_key=**APIKEY**", curl get a no response error. When I run the command in a windows terminal and in access the URL in the browser, both respond with a JSON data as expected.
So I moved the docker contained to the Host network, the container wouldn't start as it could not see the plex until I also moved plex to the Host network. After both of the Host network, I ran Kometa again and it seem to be working with no errors. I ran the curl command above in the docker console, it now responses with the JSON data.
I don't know what I did to mess with the original docker network to stop the API URL responding but happy it seems to be fixed.
Thank you @upper gust for your responses and help.