Non-forking frames in AEC

Question

Here
https://shelah.logic.at/papers/875/
on page 15, item 4 in the proof of 2.2.6, I would like to know why
$S(M)\leq \lambda \times \lambda^+$.
I understand that models in $K$ have cardinality $\lambda$ and that there are $\lambda^+$ of them.
I also understand why $\lambda^+ \leq S(M)$.