In this comment you said that you manually added the configuration to an nginx.conf file. The error message here now looks like this change is still active, although it shouldn’t be.
Did you modify the docker-compose.nginx.yml file or the files below the nginx subdirectory in the docker directory?
Please run the following commands:
cd /home/jpzone282/mattermost
cat docker-compose.nginx.yml
find nginx
And please post the outputs again.