Nyger Seed

As a novice to attracting birds to our garden I’ve placed multiple Nyger seed feeders across our garden. In the hope of attracting stunning goldfinches and hopefully greenfinches too. 
Yet in a month since doing so and using ‘fresh’ seeds I’ve yet to see a single bird attracted to Nyger seed. An experience shared by my mother in law too. 
I'm intrigued to know if the attraction of this seed is a falicy or do I need to do anything different here? 
Thanks so much in advance for any suggestions.