To expand on what @dpoulton said:
If you're only going to access this instance of Joplin Server from your local network, change APP_BASE_URL environment variable to http://192.168.1.49:22300.
If you also want to access it from a domain name, that option isn't currently supported, but may be in the future: New Install - Invalid origin error - #14 by laurent
I do want to have it both ways myself, so I will have to change the url in my sync config from local ip to domain name if I'm inside vs outside my local network (which is a pain, but at least it'll work). I also had to modify the source code in the server to bypass this origin check. I modified the isValidOrigin function to always return true in this file inside the docker container: /home/joplin/packages/server/dist/utils/routeUtils.js.