There were IAEA boots on the ground to ensure that their plutonium production (from waste products) was minimal and monitored...also, the centrifuges for uranium production were limited and monitored.
Since 2018/9 Iran has 'cheated' on the agreement...thanks to Trump's foolish decision.
Link: https://armscontrolcenter.org/the-iran-deal-then-and-now/
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