Hi there! I see you're unable to send texts and you have no audio during calls on your TextNow app using your Mac running OS X 10.15.7. Let's get to the bottom of this.

To start, could you tell me if you are connected to Wi-Fi or using mobile data on your Mac? Also, have you noticed if this issue started recently after an update or specific event? This info helps me narrow down the cause.

Meanwhile, let's try some basic troubleshooting steps:

1. Check your internet connection: Make sure your Mac is connected to a stable Wi-Fi network and that Airplane Mode is off if applicable.

2. Quit and restart the TextNow app: Sometimes restarting the app can fix glitches.

3. Update the app: Ensure you have the latest TextNow app version installed from the Mac App Store or the official website.

4. Clear the app cache and data: On Mac, this can mean quitting the app, then deleting cached files. Since the app backs up your messages and call history, this won't delete your data. Let me know if you want detailed steps on this.

5. Check microphone permissions: Since there's no audio during calls, let's verify TextNow has permission to access your Mac’s microphone. Go to System Preferences > Security & Privacy > Privacy tab > Microphone, and make sure TextNow is checked.

Try these steps and let me know what happens. If the problem persists, we can look into more advanced solutions like reinstalling the app or checking for any account issues.

Are you comfortable walking through these steps?