How to access server from outside using public IP

Hello,
When running a docker flask app on the linode server instance. I am unable to access it using the public IP. Also, I've tried some other methods but there's this same issue of not being able to access the linode servers publicly. I am also logged in as the root user so shouldn't be a permission issue. I have rebooted the server but still having the same issue. Basically, I'm able to map the docker port to the linode server port but the linode server port is not accessible from outside. So I am not able to call that as an api URL from outside.