React has nothing to do with Unity.
Like React, PHP has absolutely nothing to do with Unity.
You need to learn how to query a basic REST API.
Look for tutorials on querying a basic REST API.
In Unity, the easiest will likely be with the UnityWebRequest class.
But get the API working from the command line FIRST:
Networking, UnityWebRequest, WWW, Postman, curl, WebAPI, etc:
https://discussions.unity.com/t/831681/2
https://discussions.unity.com/t/837672/2
And setting up a proxy can be very helpful too, in order to compare traffic:
https://support.unity.com/hc/en-us/articles/115002917683-Using-Charles-Proxy-with-Unity