Empty file downloaded for subregion boundary
I receive empty file (with content: {"type" : "FeatureCollection", "features" : []} ) each time when request subregion for any country. For example Finland level 4 subregion boundary https://osm-boundaries.com/api/v1/download?db=osm20241007&osmIds=-2375170&boundary=administrative&format=GeoJSON&srid=3857
With that link you are requesting to download the polygon with id -2375170 where tag boundary is set to administrative. It doesn't exist, therefore you are receiving an empty set.
https://www.openstreetmap.org/relation/2375170 has boundary=historic.
If you want to download all children of 2375170 you'll need to use the recursive=true flag.