Do you have roaming enabled on your phone?
Roaming is free with any Visible plan!
”Roaming happens when you’re traveling in remote areas within the US, and you end up automatically using another service provider’s network. While roaming speeds can be reduced to 2G.”
To add to what GreenSub said as long as roaming is enabled on your phone Visible has what is called domestic roaming so it will use other network towers when a Verizon tower is not available. It is possible the Visible map may not be up to date. Verizon owns Visible and uses there towers so if there is Verizon coverage there should be coverage on Visible and it may only be 4G LTE depending on the area.