公民配偶婚姻綠卡轉正 I-751 要不要打指紋的錢？

我是公民，老婆的兩年綠卡轉正，751 被退了回來。說支票不對。我看了751 instruction 說

U.S. Citizen or Lawful Permanent Resident Spouse. If you are the U.S. citizen or lawful permanent resident spouse, you do not need to include a biometric services fee at the time this petition is submitted. If USCIS later notifies you that you must submit your biometrics, you will receive a biometric services appointment notice with instructions on how to submit the additional fee.

我的理解是公民配偶繳費不用交指紋費用。這個理解對嗎？ 

謝謝，