Function is not defined | Node.js

I have boleto.js

var axios = require('axios');    
function getBoleto (token) {
  if (!token) throw Error('Miss Token!');

  return axios.get(
    '/boletos',
    {
      params: {
        token: 'token...'
      }
    }
  ).then(res => {
    //console.log(res.data);
    return res.data;
  })
  .catch(err => {
    console.log('Error boletos', err);
    })
}        
getBoleto()
  .then(boletos => {
    gravar(boletos, function(err){
        if (err) throw new Error('Error boletos');
    });
  });

And gravar.js

module.exports = function (object, callback) {
// Save DB
...
console.log('Saved successfully');
callback();
}

What I need? Save the return of boleto.js in gravar.js

But brought this message : Reference error: gravar is not defined

via Diogo Barros