Failing to import custom asset into Unity, error: This type of asset is not currently supported.

Hello,
I am currently working on a project in which I aim to visualize the electoral results of the city of Madrid by coloring 3D buildings according to the most voted political party in each neighborhood. To achieve this, I have created a GeoJSON file that includes data on the boundaries of Madrid’s neighborhoods as well as the most voted party in each of them.

I uploaded this GeoJSON as an asset to Cesium ION (see image 1), and everything seemed to be in order. However, when attempting to import it into Unity as a Cesium 3D Tileset, I receive the following error message (image 2): “This type of asset is not currently supported.”

Does anyone have any suggestions on how to resolve this issue?
Thank you very much in advance.