Integrating SQL and LLM what is you experience

I was tasked with building a "native language interface" to our database. After developing it for a month, it seems to me that I hit a wall with the correctness of the resulting SQL. 80-20 would be a good estimate. My feeling is that it something that cannot be used a regular user.

Did you do better and you have tips?

NOTE: I'm not talking about performant queries only about producing a correct result. I would say that only about 50% cannot be better optimized, but I don't care about that.