Don't use negative IDs
Please don't use negative IDs within the geojson files
Reason: Some Geo-libraries and also professional software like Global
mapper refuse to load files with a negative ID. For example the boundary
of Austria has "id": "-16239" . Please change it to "16239" or some
other positive value.
Changing that would require a huge rewrite of a lot of code. It's not something that will be done the closest months at least. For us it will also affect the site we have in the other end, that's using OSM-Boundaries as its source.
It's an OpenStreetMap tool creating the negative IDs for us, and we haven't really cared about that since it works well with our own tool chain.
Until a better solution is provided I can only suggest to open the file with a text editor and replace '"id: "-' with "id: "'.