noun which may take the genitive case particle 'no'
off-book; off-the-books
Describes transactions, assets, or activities not recorded in official accounts; often implies informal or hidden dealings.
その会社は帳簿外の取引をしていた。
The company was conducting off-the-books transactions.
帳簿外の資産が発覚した。
Off-book assets were uncovered.