Exporting a .fbx file with Poliigon textures?

Dear Blender People!

I need some help, I’m using simple image textures and also the Poliigon Addon for texturing in Blender 2.91, and I’m having trouble with exporting a .fbx file - it includes all other (non poliigon) textures, but none of the Poliigon ones.
In the export window I set the Path to Copy and tick the Embed Texture button to do so. The textures are embedded in the blender file too.

Here are some files so you can see what’s the problem:

Does any of you know a solution?

Thanks!
Gergo