Debug a "browser application" running on Mac OS and converted from a Windows app

Hello, A developer coded a Windows application to open a website as if it was a standalone application, with Electron app builder. This application enables users to access a specific URL (without disclosing this URL) by clicking on a desktop application (with a .exe extension). At first step, the application ask users their username and password. It then checks if these credentials are valid by sending a query to our server. If they're valid, the application opens a VPN connection through OpenVPN to connect to a VPN service (we have a dedicated static IP). Then, it opens the target web page. It uses a specific user-agent (OS, browser, browser version, screen size, etc.) and the CSS files are loaded from our server (this way, we can make a change on these files and it applies to all users at once). If it's not connected with the specific static IP provided by our VPN service provider, it won't launch the target URL and the application will close itself. When the target URL is opened in the application, some parts of the web page are hidden, some links are deactivated, etc. (that's what CSS files are for). Note that even if the application is used on a Mac computer, the user-agent must be strictly the same than the Windows version. It's working like a charm on Windows but the developer who converted this tool for Mac users didn't do it well and she doesn't reply to our messages for almost 2 weeks now. You must have at least 1~2 years of experience on nodejs and must have experience with Mac applications. Best regards, Fab.