When a $\pi^0$ decays into photons, the only possible number of photons to which it can decay is $2\times n$, with $n$ a natural number. This is because in electromagnetic decays charge conjugation is conserved, let's assume that it decays into two photons
$$\pi^0 \to \gamma+\gamma$$
$$C|\pi^0\rangle = 1$$
$$C|\gamma\rangle = -1$$
in this decay, parity also needs to be conserved, and
$$P|\pi^0\rangle = -1$$
$$P|\gamma\rangle = -1$$
the parity of the system of two photons is given by $(-1)^lP|\gamma\rangle P|\gamma\rangle$ where $l$ is the orbital angular momentum of the system. Does this mean that if parity is conserved, the orbital angular momentum of the resulting system must be $l=1$ (or 3, 5...) or am I deducing something wrong?