BGT Citygml in Cesium Ion not working

Hi, I,m trying to add this asset to Cesium Ion but I get this error during upload:

Error: Invalid File
File: bgt_pand.gml
Additional Information: Missing spatial reference system (srsName) and no source SRS given (--source-srs).

The file is a citygml file of the BGT. PDOK BGT download viewer

CityGML files need to have a defined Spatial Reference System (SRS) for us to be able to understand the coordinates that the file is working in. It sounds like this particular file does not have an SRS defined and therefore we are unable to process it.

If you can provide the exact data you were trying to tile, we can confirm this to be the case.