Hi Muhammed,
What platform version are you building your app on? I believe the minimum version needs to be 11.12.0:
https://www.outsystems.com/forums/discussion/70801/technical-preview-seo-friendly-urls-for-reactive-web-apps/
Did you validate that your Reactjs version is 16 or higher?, the instructions in the url you shared don't always work.
What you should do is:
- Open DevTools in your reactive app (F12)
- Go to search and search on reactdom
- Click in the results and check on the source at the top the react version,

Regards,
Daniel