Add catch-all route for serving index.html

api/index.js

@@ -8,6 +8,7 @@ const postRoute = require("./routes/posts");
 const categoryRoute = require("./routes/categories");
 const multer = require("multer");
 const path = require("path");
+const __dirname = process.cwd();
 
 dotenv.config();
 app.use(express.json());
@@ -38,6 +39,10 @@ app.use("/api/users", userRoute);
 app.use("/api/posts", postRoute);
 app.use("/api/categories", categoryRoute);
 
+app.get('/*', function (req, res) {
+  res.sendFile(path.join(__dirname, 'build', 'index.html'));
+});
+
 app.listen("5000", () => {
   console.log("Backend is running.");
 });