I'm pacing the pavement of a dead-end street in Sydney's inner-west.
It's overcast and has just started drizzling as my phone rings.
"Hi, I'm a minute away," a voice on the other end tells me.
I watch as a white sedan turns into the street.
"OK, I'm down the end wearing a black jacket," I tell him.
The car pulls up and I walk around to the driver's side window.
A young man hands me a plastic bag and I give him the cash. The whole exchange takes about 30 seconds.
It felt about as shady as it sounds but this is how kids in Australia are getting their hands on illicit nicotine vapes.
"I don't want to be like a massive snitch, but it's actually super easy," 17-year-old Ruby told Four Corners.
"There's lots of small dealers doing local areas and stuff.
"You go on your phone, you're like, 'Can I pick up a vape?' and they're like, '20 minutes'. And you just meet them somewhere and they just hand it to you.
"I think it's the same as any other drugs. It's definitely word of mouth.
"Any social media as well."
Ruby is struggling with a nicotine addiction that started three years ago.
"It's the last thing you do before you go to sleep. It's the first thing you do when you wake up. Sometimes you wake up a couple times during the night to hit it," she said.
"It's totally got a hold of you and it's the only thing you think about."
Booming black market
Vaping is a multi-billion-dollar global industry. It's estimated about 400,000 people now vape in Australia.
In New South Wales alone, one-tenth of the 16-24-year-old population now vape – that number has more than doubled in the space of a year.
This is despite the fact that it is illegal to sell or possess nicotine vapes without a prescription.
An investigation by Four Corners has found there is a thriving black market, fuelled by rising demand and a failure to police the rules.
Teenagers are buying cheap, disposable vapes imported from factories in China.
We've found illicit sales on social media are rife, with hundreds of suppliers to choose from across Facebook, Snapchat, Instagram and TikTok.
Many of these dealers use code words and images to illegally sell their products to children and they offer free delivery.
Professor of Epidemiology and Public Health at the Australian National University Emily Banks said vaping is harmful to health, particularly for non-smokers and young people.
"They cause addiction. They can cause poisoning and toxicity through inhalation, which can lead to seizures, trauma and burns, lung injury," she said.
The federal government commissioned Professor Banks and her team to investigate the harms of e-cigarettes. Her report, released earlier this year, is the most comprehensive review of the global evidence so far.
"When we're talking about addiction in children, e-cigarettes may actually be more dangerous than smoking because they're much easier to access, they're much more discreet, you can hide them, and they also have these multiple flavours so they're much more appealing to children, and they're marketed to children," she said.
"Use of e-cigarettes in that younger age group isn't about giving up smoking. It's about a completely new habit."
State and federal authorities are targeting the illicit vape market.
NSW Health has raided tobacconists, seizing more than $1 million worth of stock since January.
The Therapeutic Goods Administration (TGA) has also fined individuals and online suppliers.
Despite this, the illegal market is still booming.
"It's a de facto prohibition," vaping advocate Dr Colin Mendelsohn told Four Corners.
"Every month, millions of illicit unregulated vapes are imported into Australia.
"A black market will sell to young people, they'll sell dodgy products, and they'll sell them at huge profit."
Four Corners investigated the online trade of Chinese-made disposable vapes, including a website that promoted itself as a major Australian distributor of the popular brand Gunnpod.
Gunnpod Australia claimed to supply major tobacconists as well as selling to online customers.
Four Corners ordered Gunnpod vapes and had them delivered. We also bought the brand from four of the tobacconist chains listed on the website — Free Choice, Cignall, TSG and King of the Pack.
None of these vapes listed the key ingredient – nicotine — on the packaging.
We took the devices to the University of Wollongong to confirm what was in them.
Analytical chemist Dr Celine Kelso has tested hundreds of samples and said illegally imported devices usually don't list nicotine on the packaging to evade seizure by authorities at the border.
"Nicotine is illegal in Australia, so by not having it on the packaging, it's a way for sellers to stop the seizing of the samples," she said.
Dr Kelso found the Gunnpod vapes we bought all contained high levels of nicotine.
"It's in a concentration that's as high as it comes in those kinds of devices," she said.
After getting the results, Four Corners approached the man behind the Gunnpod Australia website.
Outside his warehouse in Western Sydney, Hao Liu denied he ran a vaping business or sold Gunnpod vapes.
Within days of speaking with Mr Liu, major changes were made to the website.
It now states it "doesn't hold any stock" and that it is working to bring Gunnpod to "all pharmacies" as "the first TGA-approved vape brand in Australia".
In a statement, general manager of retailer King of Pack Lucy Soud said: "Any instances of alleged selling of nicotine e-cigarettes or e-liquid nicotine are taken seriously by King of the Pack and are investigated thoroughly.
"Frequent inspections are undertaken with both retailers and wholesalers to ensure compliance with all applicable laws and where appropriate, matters are referred to the appropriate authorities."
Cristie Bowler, national operations manager of Cignall, said all franchisees were required to sign an undertaking that they would not sell vape products including nicotine.
"We neither condone nor tolerate any of our franchised businesses engaging in the supply of illicit tobacco products," Ms Bowler said.
Children addicted to nicotine
In her final year of high school, Ruby says giving up vaping isn't easy. She's suffering from withdrawal symptoms, including cravings, anxiety and headaches.
A few months ago, Ruby confessed to her mum Nikola she was vaping and needed help giving up. She is now on nicotine patches and her mum checks in with her regularly.
"She'd tried to quit, and she couldn't. She'd had these really unpleasant symptoms that she didn't like that confused her, and she wanted me to help her find a way out of it," Nikola told Four Corners.
"I was really upset. I was really fearful for her health. I felt really angry that this product existed that seemed almost designed to appeal to kids and now she couldn't stop it."
To help her quit, Ruby asked her friends not to give her vapes, even if she begs.
"It's like a monster that takes over you. Like, I'd go up to people like 'do you have a vape?' and they're like, we can't give it to you, and I told them not to give it to me, but I get so angry," Ruby said.
"I'm like 'you're not my friend, if you really cared for me, you'd give me a vape'."
Her friend Maya told Four Corners she has seen Ruby try to give up many times.
"It's not been a linear progression, you know, just an up and down," she said.
"It is really hard. If she quits this time or doesn't quit this time, that's alright, at least she is trying."
Additional reporting by Jeanavive McGregor and Patrick Begley
Watch the full investigation on Four Corners tonight at 8:30pm on ABC TV, ABC iview or live stream on the Four Corners Facebook page.