In RepU, open your widget, choose light or dark and left or right, then click Copy next to the embed snippet.
Open index.html in your project root, or public/index.html for Create React App. Paste your code just before the closing </body> tag.
Build your app and deploy it, then open your live site to see your Google reviews.
Check your live site in a private window, not the editor or preview. A domain-locked widget only shows on your own domain.
Check you edited the index.html your build actually uses, then rebuild. If you set a Content Security Policy, allow the RepU domain.