  Let $E/F$ be a CM extension of number fields, and let $H < G$ be a unitary
Gan--Gross--Prasad pair defined with respect to $E/F$ that is compact at
infinity. We consider a family $\mathcal{F}$ of automorphic representations of
$G \times H$ that is varying at a finite place $w$ that splits in $E/F$. We
assume that the representations in $\mathcal{F}$ satisfy certain conditions,
including being tempered and distinguished by the GGP period. For a
representation $\pi \times \pi_H \in \mathcal{F}$ with base change $\Pi \times
\Pi_H$ to ${\rm GL}_{n+1}(E) \times {\rm GL}_n(E)$, we prove a subconvex bound
\[ L(1/2, \Pi \times \Pi_H^\vee) \ll C(\Pi \times \Pi_H^\vee)^{1/4 - \delta} \]
for any $\delta < \tfrac{1}{4n(n+1)(2n^2 + 3n + 3)}$. Our proof uses the
unitary Ichino--Ikeda period formula to relate the central $L$-value to an
automorphic period, before bounding that period using the amplification method
of Iwaniec--Sarnak.
