I find a lot of people esp. domestics using a slightly more commercial panel, often choose Areas to try and achieve what most of us would just use Part for.
If you can set areasa A & B with the engineers code it suggests to me that the system is programmed correctly. I'm thinking the issue is with the code you are using. Try setting up another user code for area B only.
I think what amps is saying your missing something, unassign and go through it again , as he says if b is not highlighted , one of the steps is missing
Assign all zones and see what happens perhaps
I wonder have you only tried one zone?
Is Area B assigned to the user code?
I think you are presuming that both the A & B keys will be highlighted when you enter your code. This is not always the case.
Enter your code and the A key is highlighted. If you press the B key is that highlighted?
What model is it in? I think SCB mode you would but you could stick a wireless as additional on the enforcer rear of property of other is on front
But charging current would do two I think in SCB mode