Hakka Abacus

I love to eat Hakka Abacus ever since I tried one from my inlaw's neighbour. So everytime if there's any hawker selling this, I'll surely buy but its not as good as theirs.
This is the first time I'm making this after referrring to alot of recipes shared by others.
As I've left with alot of purple sweet potatoes from the making of Ang Ku Kueh, I used sweet potatoes instead of yam.
I dont know is it becos of that, my abacus tasted like rubber. That's what my children claimed. I too find its abit hard but thankfully the taste is there.
So if I'm gona make this again, I will use yam.