You have to show the probe on its trajectory in the solar system like this:
View attachment 98338
In this case I've chosen the first mark and I'm at 7301 m/s, above the specified 7250 m/s for that mark. The threshold corresponds to the liberation speed.
However if you use the VanillaUpgrades mod you can simply show that your eccentricity is above 1.0, the distance doesn't matter then.