server.js

  // base route
  app.put("/:user", function (request, response) {
    collection.updateOne({ user : request.params.user },
                         {$set:{ ...request.body, user : request.params.user }},
                         function (err, r) {
      if (err){
        response.send("An error occured") 
      }else{
        response.send("All well")
      }
    })
  });

s/occured/occurred ?