const options = {
  method: 'PATCH',
  headers: {Authorization: 'Bearer <token>', 'Content-Type': 'application/json'},
  body: JSON.stringify({role_ids: ['<string>']})
};

fetch('https://api.keystoneos.xyz/v1/platforms/me/members/{user_id}', options)
  .then(res => res.json())
  .then(res => console.log(res))
  .catch(err => console.error(err));

{
  "user_id": "<string>",
  "email": "<string>",
  "name": "<string>",
  "picture": "<string>",
  "roles": []
}