A very common problem can be this:
Bind your app inside Docker to 0.0.0.0, not to 127.0.0.1 address to let Docker reach the app inside container.
UPD: Don’t try to solve it with docker. There is no docker command to fix that. It strictly depends on the using app, web-framework, etc. Read the manual of the tool you use inside the container. Try to google “how to bind [using framework] to the specific address and port”. It could be an environment variable, cli parameter, code, etc.