Set a custom user greeting using RingCentral SDK in Node.js

I'm trying to set a custom user greeting using the RingCentral SDK but every method I try gives me the error "unsupported media type". It would be very helpful if someone could provide an example of how to generate a request for this endpoint using the RingCentral SDK in Node.js. My current code is attempting to use another Node.js package to read file contents.

platform.on(platform.events.loginSuccess, function(e){
    console.log("User logged in successfully");
    set_greeting(get_file());
});

async function set_greeting(binary) {
    console.log(binary);
    try {
      var resp = await platform.post('/restapi/v1.0/account/~/extension/~/greeting', {
        'type': 'Introductory',
        'binary': binary
      });
      

      var jsonObj = await resp.json();
      console.log('Greeting set successfully.');
      console.log(jsonObj);
    } catch (e) {
      console.log(e.message);
    }
  }

async function get_file()
    let binaryData = fs.readFileSync('C:/Users/user/Desktop/RingCentralApps/project/example.mp3', "binary");
    
    return binaryData;
}