When uploading a Texture Maps in a Material Variant, it will always return this in the output window. This applies to all Texture Maps.
[The error icon says “Failed to upload”]
Although, you can open the Material Variant inside the MaterialService in the Explorer and inside the Properties Tab, you can upload there the Texture Maps. The downside is that the images are saved to the game, meaning you will see them listed in the Image Changing Popup.
Expected behavior
Well, it shouldn’t print any errors in the output window and it should just be applied in the Material Manager with the Asset ID written.