I think you have been misadvised.

There are a number of conditions around trade UuA, so you mustn't use On Business, it's all got to be BA prime numbers, issued on 125 plate. And obviously there has to be Avios availability. The fare buckets are fine, there are some deep discounted BT and IT tickets which would be ineligible for UuA, your travel agent should be able to tell you if they were BT or IT, but on the face of it unlikely. The more usual "deep discount" issue applies only to WT tickets, so unless there are other factors involved the agent you were talking to was getting confused with that. But to be clear I and R are fine for UuA. You may be able to do it online, but usually it's a BAEC specialist that has to do this, and therefore you need to talk to someone competent in that area. It's usually codeshares and 001 plating that gets in the way here.