App proxy or API urls doen't work if we use "Sentence case" in "App Name"

[NahianAlJaber]

I am new Shopify app developer.. Here are one of the configurations of my shopify app:
App name configurations:
App name: app_dev_2
App handle: app_dev_2

App Proxy settings:
Subpath prefix: apps
Subpath: app_dev_2
Proxy url: https://015d-182-163-107-41.ngrok-free.app/v1

The problem is, with above configurations, our app works. But If we use app name as sentence case like "App dev 2" or "App dev" instead of "app_dev_2", our apps doesn't work. What is the problem? Because we can have app name as sentence case. But with app name as sentence case, our app proxy or app API url doesn't work!

Not working config:


Working config:

I am so confused! 
Question 1: Should we always use app name as handle or proxy subpath? Then we can't use sentence case with App name!
Question 2: Can't we use sentence case in app name?
Question 3: What are we missing?

Thanks