I would love to say its Safari because that is already installed on your Mac. However, it’s not.
In a recent update, Apple added this very annoying feature which forces you to click Allow every time you need to check in or check out a document.
This issue is not unique to NetDocuments.
That leaves us Google Chrome and FireFox.
First, we need to make sure you have installed ndoneclick.
FireFox
Google Chrome
https://chromereleases.googleblog.com/2018/01/stable-channel-update-for-desktop_24.html