TIER has different zones in which you can either park, or end your ride.
In general you cannot end your rental in red areas. You can however temporarily park your TIER bike, lock it, run some errands and come back later to unlock your bike and continue your ride. In busy city centers, like the center of Utrecht and Almere there are special zones in which you can end your rental or temporarily park your TIER bike.
Go to the map in Gaiyo and select a TIEr bike, or go to your active ride, and the red zones should immediately be visible. You should also see purple area's although these are not available in every city. In a purple area you are allowed to end your rental or park your bike temporarily whenever and wherever you like.