Scale mobile app

currently have a mobile app that does REST calls to a express js backend. I am going to build a chat feature on the app using and was wondering if I should just use my current express js backend for or create another separate express js server to handle the Which option is better to scale to thousands of users?

Just put it in your old project, but make sure it will be eas to seperate it to its own project (Dont entangle the code, give its own endpoint etc) if the need arises. KISS

great point thanks for the advise!