How can I get my Vitra Low Flow cistern to fill with water?

I tried to flush my Vitra toilet this morning, but the cistern (tank) did not refill with water. The tank is empty and won't refill. The water tap is on full, but by pushing both sides of the button, the tank would not fill. What do I do?
Phyllis Bertin, May 2017


done
I followed instructions to remove lid and fixed it. All is good. thank you.

Phyllis B., May 2017