When updating a contact via the public API, properties that couldn't be applied are now reported back to you instead of being silently dropped. Previously, sending a property by its display label (e.g. "Call Attempts") instead of its internal field name returned a success response even though the value was never saved. The response now includes a rejectedProperties list naming each property that was skipped and why, and when you've used a display label it tells you the correct internal name to use. This reporting covers all custom property types, including multi-select properties.