subscribe.js

// lambda function in Netlify Functions to add "subscribed" role to user
const axios = require('axios')

function subscribeUser (url, token, id) {
  return axios({
    method: `put`,
    url: `${url}/admin/users/${id}`,
    headers: {
      'Authorization': `Bearer ${token}`, 
      'Content-Type': 'application/json',
    },
    data: {
      app_metadata: { roles: [`subscribed`] }
    }
  }).then(response => {
    console.log("RESPONSE", response)
    return response.json()
  }).catch(error => {
    console.log(error.response)
  })
}

exports.handler = function(event, context, callback) {
  const data = JSON.parse(event.body)
  return subscribeUser(data.url, data.token.access_token, data.id)
}

Getting response:

data: { code: 401, msg: 'User not allowed' } }