Kernrechtsfrage
Whether the cantonal surveillance authority lacked subject-matter jurisdiction and its decision was therefore void
Extrahierter Entscheid
The authority was not competent under federal law, but the defect did not amount to qualified incompetence causing nullity; the decision was only voidable and no annulment was warranted.
Extrahierte Begründung
Although modification of divorce-based child support belongs to the divorce judge, the cantonal authority acted as last cantonal appeal body under cantonal law. Since the parties did not timely contest jurisdiction and the defect was not of a nature requiring ex officio nullity, the decision stood.