If you want to deploy an application with Express, Node.js, & MongoDB for the backend. HTML, CSS/Sass, and JS are used in the front-end. Then Deploy firstly the backend on the Render as explained in this blog and get the deployed URL of the back-end. Then add that URL at every hit point of the backend in the frontend application. Like below :-
//before const res = await axios.get("/api/posts/" + path);
//After adding const res = await axios.get("blogap-fsd-wr32.com/api/posts" + path);
And then deploy the frontend part as explained in my blog : anuragk24.hashnode.dev/how-to-deploy-static-websi…
🚀And your application will deploy successfully. Thank you😊.