Hi there! I understand you’re having trouble getting live Hallmark through your cable subscription on your Mac running OS X 10.15.7. Let's see if we can get this sorted out.

To start, may I ask:
- Are you trying to watch live Hallmark through a web browser or through the Hallmark+ app on your Mac?
- Have you successfully logged in with your cable provider credentials on the Hallmark+ site or app?
- Have you noticed any error messages or does the live stream just not appear?

With those details, I can give you the best tailored advice. Meanwhile, here are some general steps we can try:

1. Verify Your Cable Subscription Access
Double-check that your cable subscription includes the Hallmark Channel live streaming rights. Sometimes, even if you have cable, the live Hallmark Channel may not be part of the package or streaming rights.

2. Log Out and Log Back In
If you are using the Hallmark+ app or website, try logging out completely, then log back in with your cable credentials. This can refresh your authorization.

3. Browser Check
Since you’re on a Mac, ensure your web browser is fully updated. For Safari, go to the Apple menu > System Preferences > Software Update to check for any pending updates that may include Safari patches.

4. Clear Cache and Cookies
Sometimes cached data interferes with live streaming. Try clearing your browser’s cache and cookies and then reload the Hallmark+ website.

5. App Reinstallation (if using the app)
If you are using the Hallmark+ app on your Mac, uninstall it completely, restart your Mac (wait about 10 seconds after powering down), then reinstall the app fresh from the App Store.

6. Network Check
Check your internet connection speed and stability. A slow or unstable connection can prevent live streams.

7. Alternative Browser
If streaming doesn't work in Safari, try another browser like Chrome or Firefox to see if the issue persists.

If after these you are still not able to stream live Hallmark via your cable subscription, there might be an issue with authentication or your provider’s integration. In that case, contacting your cable provider to confirm your live streaming rights and mentioning the Hallmark app might help.

Let me know what you've tried or observed so far, and I’ll guide you further!

Are you watching through the Hallmark+ website or an app? And do you get any specific messages when attempting to watch live TV?