。
It's a bribe for the official.
Literal
Official [to-への] sleeve [gen-の] underneath [copula-だよ].
袖の下 ('under the sleeve') is the classic Japanese idiom for a bribe — from the old custom of passing money hidden inside a kimono sleeve. A vivid image preserving pre-modern Japanese corruption practices in the language. への marks the recipient of the bribe; note the へ+の stacking is standard for 'to-[gen].'