Sen. James Lankford on Thursday demanded answers from President Obama on the $1.7 billion in cash payments he made to Iran, and said people “deserve to know the full extent” of the controversial payment.

The Oklahoma Republican wants the president to answer 13 questions by Sept. 19, including why the payments were made in cash, whether Iran had requested cash, if there were worries that cash could not be tracked in the way a wire transfer could, and if there are any other settlement negotiations underway with Iran.