need a detailed answer please! minimum 600 words

Ivan is an international fish supplier based in Russia. One of Ivan's biggest clients is Robert who is based in the United States (U.S.). Over the years Ivan and Robert have entered into various common law contracts where Ivan has sold and exported Russian fish and seafood to Robert in the U.S. In November 2021 Robert and Ivan entered into new negotiations for the supply of Russian fish and seafood. The two parties agreed on a supply contract where Ivan would export 5000kgs of Alaska Pollock and 3000kg of red king crab, all sourced from Russian waters, to Robert in the U.S. The contract was to be performed in phases, requiring Ivan to ship a load of the seafood every three months and ensure that they had completed the entire load by June the following year. As part of the agreed terms of the contract Robert had to pay the entire contract amount of $750,000. At the start of December 2021 Robert paid the entire $750,000 contract amount into Ivan's account. Ivan confirmed receiving the sum and notified Robert that he was in the process of preparing the first shipment of seafood, which included 2000kg s of Alaska Pollock and 500kg of red king crab, all valued at $200,000. The first shipment of seafood arrived in the U.S. in Feb 2022 and was received by Robert. A few weeks later in March 2022, Ivan was in the process of finalising the second shipment of seafood when the U.S. government passed a law banning all Russian seafood imports. Following the ban, Ivan has not been able to send any other shipments and has refused to refund Robert. Robert is not sure about the legal implications of the ban on his contract with Ivan and his money. By referring to the common law of contract, advise Robert. (30 Marks)