Former UK ambassador Sir Richard Dalton wrote a piece back June 2016 in Asian Affairs explaining seven problems with the implementation of the JCPOA.
The very first item on his list, is:
not re-authorizing U-turn transactions in dollars (for reasons related to current US politics), thereby maintaining a sanction that was originally enacted to get Iran to negotiate seriously;Full article: THE IRAN NUCLEAR NEGOTIATIONS: ONE YEAR ON (tandfonline.com)
Why were dollar U-turn transaction sanctions not removed? An Iranian newspaper explains:
Why was the U-turn sanction not lifted in the JCPOA, and why is requesting “related services” necessary? A U-turn transaction means Iran’s indirect use of the US financial system leading to Iran’s assets in dollars to be filtered in US banks. The dangers of this are clear for Iranian banks and the government, and it has become even more clear in recent days.
In case Iranian assets are filtered in US banks, they face two threats: The first one is [the risk of] being confiscated due to the initial sanctions of the United States, and in particular the Executive Order 13599 which still stands, and the second one is being confiscated on account of the US plaintiffs’ demands which as a result of the so-called Iran terrorism compensation case files have acquired verdicts against Iran and are looking for Iranian assets to execute the verdicts from that source.
With these two threats in view, accepting U-turn transactions as a privilege – what the critics of the JCPOA insisted upon in the early days of its publication – could result in the loss of some of Iran’s foreign assets and financial institutions…
Making use of the dollar as long as US banks do not get involved is acceptable; but where the money is kept and filtered in US banks, we will be facing the risks mentioned earlier. What the authorities in the administration have said in recent days is that when P5+1 countries made a commitment that transfer and conversion of Iranian foreign exchange assets from one place to another (except the United States) is permitted, and there are no obstacles, and related services will be available to Iran, they must do everything necessary to provide the ground for their conversion. You cannot say conversion and transfer are allowed but what makes the conversion possible or much easier is not allowed.
This is the promise that the United States and other countries involved in the negotiations have made to Iran and now they have to fulfil it. How? That is their business.
Source: Text of unattributed commentary, entitled: “Breaking Point of Exchange Transfer”, published by website of Iranian business newspaper Donya-ye Eqtesad on 1 June, translated by BBC Monitoring]
Note that Iran’s Central Bank head Seif came to Washington DC in April 2016 to complain about lack of access to int’l banking under the JCPOA, stating that Iran had received “almost nothing” from the JCPOA since its implementation – and that blew up in Iran among critics and hardliners who thought President Rouhani had sold out the country.
The US media also attacked Obama for supposedly engaging in a “secret agreement” to help clear dollar transactions.