What it means

TomTom 'Route not possible' (or 'TomTom can't find a route to your destination') means it couldn't work out a way there with your current settings.
Usually that's a routing restriction you've set — avoid motorways, avoid tolls, a truck or camper profile — or a destination that isn't on a road the map knows, or a map that's out of date for that area.
The destination itself is usually fine; the constraints around it aren't.

Affected Models

TomTom GO, GO Discover, GO Supreme, GO Essential
TomTom Start and Via series
TomTom Rider (motorcycle routing options)
TomTom Trucker / camper-profile devices

Common Causes

Route options set to avoid roads that are the only practical way — avoid motorways on a long trip, avoid ferries to an island
A truck, bus, or camper vehicle profile banning the device from roads a car could use
The destination pin dropped on a pedestrian area, a private road, or out in a field
An island or remote place that genuinely needs a ferry the device is told to avoid
An old map missing a new road that connects the area

How to Fix It

Check your route options.

Settings > Route Planning (or Planning).
Temporarily switch off 'avoid motorways', 'avoid toll roads', and 'avoid ferries', then try the route again.
One of those is the blocker more often than not.
Check the vehicle profile.

If the device is set to truck, bus, or camper, it avoids roads with weight, height, or width limits.
Switch it to 'Car' as a test — if the route appears, the restriction is real and you'll need to plan around it.
Choose the destination a different way.

Instead of an old favourite or a dropped pin, search for the actual address or a named place nearby.
A pin that landed on a footpath or a private track can't be routed to; picking a proper address on a real road fixes it.
Aim for a nearby point and finish on foot or by eye.

Set the destination to a junction, car park, or street near the place and navigate the last stretch yourself.
Handy for pedestrianised town centres and anywhere the device simply won't drive you right to the door.
Update your maps.

A missing new road, or a one-way system that's changed, can make a route impossible on an old map.
Run a map update through MyDrive Connect — or over Wi-Fi on newer GO models — and try the route again.