I have a proxy error when starting React, Node app - node.js

Question

Hi there just playing around with React/Node and adding a proxy into the client package.json file. However getting the following error. The react package versions are:
"react": "^18.2.0",
"react-dom": "^18.2.0",
"react-router-dom": "^6.3.0",
"react-scripts": "5.0.1"
So it runs through the startup process but exits with the following error.
[0] Server is listening on port 5000...
[1] Invalid options object. Dev Server has been initialized using an options object that does not match the API schema.
[1] - options.allowedHosts[0] should be a non-empty string.
[1] npm run client exited with code 1
--> Sending SIGTERM to other processes..
Thoughts????
{
"name": "client",
"version": "0.1.0",
"private": true,
"dependencies": {
"#testing-library/jest-dom": "^5.16.4",
"#testing-library/react": "^13.3.0",
"#testing-library/user-event": "^13.5.0",
"history": "^5.3.0",
"http-proxy-middleware": "^2.0.6",
"react": "^18.2.0",
"react-dom": "^18.2.0",
"react-router-dom": "^6.3.0",
"react-scripts": "5.0.1",
"styled-components": "^5.3.5",
"web-vitals": "^2.1.4"
},
"scripts": {
"start": "react-scripts start",
"build": "react-scripts build",
"test": "react-scripts test",
"eject": "react-scripts eject"
},
"eslintConfig": {
"extends": [
"react-app",
"react-app/jest"
]
},
"browserslist": {
"production": [
">0.2%",
"not dead",
"not op_mini all"
],
"development": [
"last 1 chrome version",
"last 1 firefox version",
"last 1 safari version"
],
"proxy": "http\\localhost:5000"
}
}