Iowa Code § 622.77: Proceedings for contempt.

Before a witness is so liable for a contempt for not appearing, the witness must be served personally with the process, by reading it to the witness, and leaving a copy thereof with the witness, if demanded, and it must be shown that the fees and traveling expenses allowed by law were tendered to the witness, if required; or it must appear that a copy of the subpoena, if left at the witness’ usual place of residence, came into the witness’ hands, with the fees and traveling expenses above mentioned.