The cancellation-policy can be queried to answer the questions:
If I cancel my service, when will it be technically decommissioned? If I cancel my service, until what date will I be charged?
When the query parameter decommision_at is not provided
it will provide the first possible cancellation date
and charge period if cancelled at above date.
The granularity of the date field is a day, the start and end of which are to be interpreted by the IXP (some may use UTC, some may use their local time zone).