"Add existing users" does not show… | Apple Developer Forums

I have uploaded one app via

Xcode

on the store. After that I went to itunesconnect.com and login with Apple ID.

Then clicked on

My Apps -> Select my app -> TestFlight

Clicked on Version of app which I want to test. And

Provide Compliance

and

Start Internal Testing

Now I need to add tester, clicked on

Add Existing Users

, but It is not showing checkbox.

Can anyone know about this ? I have tried by many time refresh the page, logout and login again, via different browsers, but no any luck.
I have posted question on other community as well, but didn't get answered yet. Please check image here.
https://i.stack.imgur.com/pXhkF.png

"Add existing users" does not show checkbox to select user on itunesconnect