Hi there! Sorry to hear you're having trouble logging into the Vestiaire Collective app on your Mac. To get a clearer picture, could you tell me if you’re seeing any specific error messages when you try to log in? Also, have you tried logging in via the website to see if the problem happens there too?

Meanwhile, here are some steps you can try to troubleshoot the login issue on your Mac (OS X 10.15.7):

1. Check your internet connection to make sure it's stable and working well.
2. Verify your email and password are entered correctly. If you’re unsure, try resetting your password through the app or website.
3. Clear cache or cookies if you’ve tried logging in via a browser, or if the app stores temporary data.
4. Update or reinstall the app: Make sure you have the latest version of the Vestiaire Collective app. If you do, try uninstalling and reinstalling it.
5. Try logging in through a web browser (like Safari or Chrome) on your Mac to see if the issue is app-specific.
6. If you use any VPN or firewall, try disabling them temporarily as they might block login requests.

If you've already tried these and are still stuck, let me know exactly which steps you've done and any error messages you see, so I can dig deeper with you.

Does that sound good to start?