The UAE also has another major role in Iranian trade - banking. You can't follow documentation properly with the Iranian banking system. There are too many restrictions on exchange. These restrictions are borne of American sanctions. International trade transactions are normally made in dollars, and all dollar transactions must go through banks in New York.
American sanctions forbid dollar transactions with Iranian participants.
To get round the problem, European banks effect transactions on behalf of Iranian banks. Debits and credits are transferred to these unnamed accounts via the European bank's usual American correspondents in New York. With only the account number to show on the documentation, no one in the United States is any the wiser as to who the recipients are. Without this mechanism, Iran would be cut off from the international trading community. Iranian banks pay extra commission.