Grammar is LL(1) or not?
That website uses a different notation than what you assumed. This would be the correct input:

S -&gt; A S | b.
A -&gt; S A | a.


You entered AS (and SA) which it does not recognize as A followed by S, but as a single nonterminal named AS.

With that input it correctly says that the language is not $\text{LL}(1)$.