Trump made it perfectly clear: No one will buy Iranian oil and still do business with America. That includes China.

Two Trump administration officials said on Friday that neither a wind-down period nor a short-term waiver on China’s oil purchases from Iran are being contemplated after Washington surprised Iran’s customers on Monday by demanding they halt the purchases by May 1 or face sanctions.
The administration has been clear to China, Iran’s top oil consumer, about no additional waivers to the sanctions after the ones granted last November, one of the senior officials said.

No additional waivers. No wind-down period.
It's clear and final.

Do you know who else is clear and final? China.

China is buying Iranian oil in defiance of US sanctions and providing what Tehran hopes will be a financial lifeline for the country’s buckling economy.

Although Beijing customs data show crude purchases from Iran are down month-on-month, China is still importing Tehran’s oil despite US measures designed to cut exports to “zero”.

Last week the Chinese received their first delivery of an Iranian oil cargo since the Trump administration in May scrapped exemptions on Iranian sanctions.

So Trump is a big, tough, strongman. So what do you think he's going to do when he's challenged?
He's going to fold.

But according to three U.S. officials, the department’s Iran czar, Brian Hook, and his team of negotiators have discussed granting China a waiver to a 2012 law intended to kneecap the Iranian oil industry. The alternative is allowing China, which recently welcomed a shipment of approximately a million barrels of Iranian oil, openly to defy U.S. sanctions.
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The 2012 Iran Freedom and Counterproliferation Act targeted the Iranian shipping, shipbuilding and energy sectors, requiring states or companies that wish to import Iranian oil and conduct business with the U.S. to obtain waivers from the U.S. government. A separate law targeted purchases, rather than imports of that oil.

Officials say the State Department is discussing an arrangement that would allow China to import Iranian oil as payment in kind for sizable investments of the Chinese oil company Sinopec in an Iranian oil field — and administration officials have offered to issue a waiver for the payback oil in official correspondence between the State Department and Sinopec, according to a source familiar with the situation.

The waiver is merely a face-saving measure. China is going to continue to defy the sanctions one way or another.
And if China gets a waiver then India will too.
As it stands, India has halted buying Iranian oil, but that has just pushed them into buying more Russian oil.