IRDのサイトによると

If you have a loss from a business leave the box blank because, we'll treat it as nil.

If you and/or your spouse or partner have business income you will need to provide verification of this each year. We’ll use your individual tax returns (IR3). If you haven’t filed your returns, we’ll ask you to send us a copy of your completed financial accounts or budgeted accounts for the coming year. We need to receive the verification of your business income in February (or earlier) to continue your payments after 1 April.

とあるので損失でなければ、ビジネスの所得も証明する必要があるようです。
IRDのオンラインアカウントをお持ちでしょうから、直接問い合わせたほうが良いと思います。