Just to make sure you’re following all the required steps.
In the Tablo Settings screen, click on the ‘Edit Channel Lineup’ button.
Click on the ‘Rescan’ button.
When the rescan is finished, click on the ‘Add to Guide’ button.
When it takes you back to the Tablo settings screen, it’s still working on downloading the guide data, and Live TV channels probably won’t work properly.
You have to wait until the guide data completely downloads, which usually takes 2 passes.
Here’s a recent post explaining that part:
If all else fails, try changing the zip code to one that is near your actual zip code via the ‘Edit Location’ button, and perform the above steps again.