Treasury generally ask for a personal postal or email address to confirm eligibility "and to contact you". You should send these details privately, not through FYI.org.nz where they would be published. You should also not allow them to correspond with you about the request over private email, as then other users cannot help you and the context of the request is lost.

1. When providing your personal details, include words to the effect of: "These details are provided solely to confirm my eligibility under the Official Information Act s12(1). Do not use these details for any correspondence or clarification about the request. For the purposes of OIA s16(2) my preferred way of receiving information is by email reply to the FYI.org.nz address from which you received the request. If you send correspondence to my private address you will be asked to re-send it to the FYI.org.nz email address, where it may still be published."
2. Add an annotation to your request outlining that you have provided them eligibility information directly.
3. If you do receive contact (email, postal) bypassing FYI.org.nz, ask them to re-send it by email to the FYI.org.nz address as you have asked. Add an annotation to the request noting this happened.