This is an expected behavior for Geocoding when only the postal code is provided as input, as detailed in https://issuetracker.google.com/73030863 and https://issuetracker.google.com/75985322, because a 4-digit or 5-digit number can often represent multiple locations(ambiguous query), even within a single country.

As a workaround, consider using Component Filtering and/or Region Biasing to narrow down your results.

This request with component filtering (postal_code & country) returned results: https://maps.googleapis.com/maps/api/geocode/json?components=country:US|postal_code:11707&key=YOUR_API_KEY