Yes, if you read my post, I said 'a piece of advice' is fine. I translated this as 'do you want good advice' and a box popped up which 'helpfully' told me that my grammar was incorrect and I had missed the article 'a' i.e. I should have written 'do you want a good advice'. I was merely saying that 'a good advice' is not correct (and duo should not be telling people that it is!). However, I reiterate, 'a good piece of advice' and 'a piece of good advice' are grammatically correct.