Hi Alexander,
Please see:
Test data(input/output/QGIS)
5077-TopoJson -TopoJson.zip (9.3 KB)
If the input is not valid - this is .json extension , please give me valid .json sample for TopoJson
that I will make full…...make full tests to all others formats. Thanks, Professionalize.GIS...standards‑compliant TopoJSON file that you can use for testing...