Conditional areas can be set on default or voyage specific level. A limited number of no go areas are enabled by default.
The most common areas are already added in the API and can be found here. This way you can find the area ID which can be inserted included in requests.
In a voyage request the custom area ID can be disabled under – voyage request – type of request – restrictions – conditional areas (see screenshot).
You are also able to set custom areas by defining your own area based on coordinates and use this area in route requests as an area to avoid or have a speed limitation.