Changing proxy in package.json is not working

I created a project using create-react-app and this one is running on http://localhost:3000/

when i want make a request to http://localhost:3090/ from my application i am setting proxy in my package.json file which is not working

componentDidMount() {
     fetch('/api/si')
      .then(response => {
        console.log(response);
        return response.json();
      })
}

package.json

"proxy":"http://localhost:3090/api"

here my expected call is localhost:3090/api/si but it's pointing to 3000 which is my client server. I tried multiple combinations nothing works

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