First, it was the #AmazonCoat. Then it was the #AmazonLeggings, followed by the #AmazonBathingSuit.

Now the #AmazonNightgown — a billowy, boho dress that retails for under $30 — has taken Instagram and New York City by storm.

“The name cracks me up, but I am a huge fan,” said 28-year-old Katie Kennedy, who bought the light-blue version a few weeks ago.

“I wear it weekly,” added the Upper East Sider. “On Friday, I showed it to the vice president of marketing at the firm I’m interning for this summer, and she bought four on the spot.”

Made by R.Vivimos, a fast-fashion brand based in China, the dress has become a cult hit among influencers. There are currently 15 different print and color combinations available on Amazon.

It’s also sold through R.Vivimos’ own website, but it’s the Amazon hashtag that’s gathering a whole tribe of fans on social media.

Search for it on Instagram and you’ll find women swanning about in Toronto, London, Brooklyn, Washington, DC — and the preppiest of vacation spots: Nantucket, Kennebunkport and Palm Beach.

Brooklyn-based blogger Grace Atwood, 37, catapulted the item to fame after dubbing it the #AmazonNightgown.

“I thought it was funny,” she said. “Plus, my dad was like, ‘What is that, pajamas?’ ”

“Most of these brands are very unrecognizable names,” Atwood said of the trend to dub items #Amazon this or that. “I think it’s just easier to say, ‘Oh, that’s my Amazon dress.’ ‘That’s my Amazon coat.’ I could not tell you who actually makes these things.”

She bought four versions of the dress earlier this year.

“I started Instagramming about it, people started sending me photos of them wearing it and I started resharing,” she said.

It made an impact: When readers of her blog, The Stripe, click on a link to the dress, she receives a 6 percent kickback from Amazon for each sale. So far, Atwood revealed, she has “sold” more than 1,000 of the frocks.

She said people can’t resist getting a lot of look for a low price.

“Years ago, my girlfriends and I went to a beautiful vintage show in New York and were looking at these gorgeous Indian tunics and they were $500,” Atwood recalled. “Now I can get this for $30!”

“It looks more expensive than it actually is,” said Lee Davidson, an events manager for Mac Cosmetics. “You never know if a $30 dress will fall apart.”

She pointed out that the “nightgown” is true leisure wear, emphasis on leisure.

“I love to feel like I live my life in pajamas anyway, so it was something that spoke to my soul,” said the 38-year-old Weehawken, NJ, resident, who bought three versions of the dress. “The patterns are so vibrant, you can’t really see wrinkles.”

“I wore it today and already got six compliments,” she added.

Still, it is essentially a shapeless, far-from-figure-flattering sack.

“I absolutely love it,” Kennedy said. “My husband does not.”

The New York Post may be compensated and/or receive an affiliate commission if you buy something through our links.