Exercise Tracker problems

Tell us what’s happening:
When comparing my API’s results from the provided example, they appear to be the same, yet all the tests relating to POST /api/users/:_id/exercises and /api/users/:id/logs fail.

Your project link(s)

Here’s what the whole meat of my code looks like. I don’t use an external database by design. Is that the problem ?

const users = []
const logs = []

app.route('/api/users')
  .post((req, res) => {
    var id = Math.floor(Math.random() * 16777215).toString(16);
    while (users.find(x => x._id == id))
      id = Math.floor(Math.random() * 16777215).toString(16);
    var user = { username: req.body.username, _id: id}
    users.push(user);
    logs.push({_id: user._id, username: user.username, count: 0, log: []})
    res.json(user);
  }).get((req, res) => {
    res.send(users)
  })

app.post('/api/users/:_id/exercises', (req, res) => {
  if (logs.find(x => x._id == req.body[':_id']) && 
     users.find(x => x._id == req.body[':_id']))
  {
    var log = logs.find(x => x._id == req.body[':_id'])
    var exercise = {
      description: req.body.description,
      duration: parseInt(req.body.duration),
      date: new Date(req.body.date).toDateString() || Date().toDateString()
    }
    log.count++;
    log.log.push(exercise);
    res.json({
      _id: log._id,
      user: log.username,
      date: exercise.date,
      duration: exercise.duration, 
      description: exercise.description
      })
  }
  else
    res.send('wrong ID')
})

app.get('/api/users/:id/logs', (req, res) => {
  var log = logs.find(x => x._id == req.params.id)
  res.json(log)
})

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Challenge: Exercise Tracker

Link to the challenge: