Can't connect to uvicorn running in docker container

This command runs, and allows me to hit my API on localhost:

uvicorn server:app --reload

However, when I run this in a docker container, I get an ECONNREFUSED (or socket hang up in postman).

uvicorn server:app --host 0.0.0.0

Curl returns this:

curl: (52) Empty reply from server

I can see this in the logs:

Uvicorn running on http://0.0.0.0:8000 (Press CTRL+C to quit)

I am mapping the default port (8000) when running the docker container, docker ps shows:

0.0.0.0:8000->8000/tcp

Is there something obvious I am missing? If not, how can I start to troubleshoot this issue?