How to connect to application running in docker

Hello,
I would like to ask how to connect to next.js application that is running inside docker container ?
I have exposed ports 9998 and 9999, and I can see Envy web UI in http://127.0.0.1:9998/ but I can see no service here, just empty UI. The Next.js app is also running, but in the web dev console in browser I can see logs like: `WebSocket connection to 'ws://127.0.0.1:9999/web/playground-nextjs:client' failed`. On the server log, there is `No viewers connected` message.
Thank you for answers.