By Shan Li

BEIJING -- On her first trip to China, 30-year-old Courtney Newnham from Portland, Ore., eagerly lined up at a street pushcart to buy a skewer of candied hawthorn berries, a traditional snack.

Then she realized nobody was giving the pushcart guy money. "Everyone was just scanning and walking away, and I was like, 'Wait, what?' " she said. She left empty-handed.

China was never an easy place for tourists, but lately just about everything seems to have gone square-shaped -- as in the payment-app QR code needed to unlock much of the Middle Kingdom.

It's how people hail taxis, consult doctors, pay for meals and book flights. Even beggars are asking for money via QR code. Not needing a wallet has simplified life for China's 1.4 billion people, but it can leave the 140 million tourists arriving in the mainland each year helpless.

They can't rely on familiar apps. Google is blocked in China. Uber has ceded the field to local ride-hailing app Didi. Yelp doesn't operate in China.

The dominant payment platforms -- Tencent Holdings Ltd.'s WeChat Pay and Ant Financial Services Group's Alipay -- have been near-impossible to use without a Chinese bank account.

Credit cards are no big help. On a family vacation, Alex Lee, 44, took his father and brother for massages at a spa in Hangzhou. When he handed over his credit card, the receptionist dug out a card reader from storage and then stared at it like an alien artifact.

"She was swiping it backward, forward, horizontally, vertically," said Mr. Lee, the co-founder of a startup in Sunnyvale, Calif. He finally showed her how to run the thing.

Susanna Sjogren, a 50-year-old teacher from Stockholm who has taken several vacations in China, said with each visit, the country has become harder to navigate.

First it was a shopkeeper at the Great Wall who wouldn't take cash for a bottle of water.

Then she managed to use a 50-yuan note, or about $7, to pay a taxi driver, but had to give him a big tip because he could only provide change through WeChat Pay.

"Ten years ago it was cash for everything. Now it's WeChat for everything," Ms. Sjogren said. "I'm getting used to being a dinosaur in China."

Foreigners aren't the only ones bewildered by China's fast transition to a cashless society. "I can't even eat!" said Gong Cheng, a 61-year-old retired Shenzhen auto mechanic, who has resorted to asking strangers to pay for his takeout noodles and then giving them money.

Josh Copley, a South African who teaches English in Beijing, said he lost touch with his family for two days when he arrived because WhatsApp and Gmail weren't available.

A few weeks later, Mr. Copley, 25, was stranded outside a bar at 4 a.m. He finally begged a Chinese couple to call him a taxi on a local ride-hailing app and repaid them in cash for the fare.

Elena Shortes, a 20-year-old college student who spent the summer studying in Beijing and Dalian, said she had to find a Chinese friend every time she did laundry, because the washers and dryers in the dorm designed for foreign students only accepted WeChat Pay.

"We felt like little kids who couldn't do anything by ourselves," said Ms. Shortes, a junior at Clemson University in South Carolina. "We always had to say, 'Please help us!' "

Shanghai-based UnTour Food Tours skirts the problem by having its guides help travelers pay for snacks and souvenirs, said Kyle Long, a co-founder.

That's no help for young people who want to travel independently. "They have to join a tour group," said James Liang, chairman of Chinese travel giant Trip.com Group Ltd., at a tourism conference.

Regulators are trying to help. The People's Bank of China has declared it illegal for businesses to refuse cash. The bank's Shanghai branch recently said it was examining payment barriers for foreigners.

Tencent last week announced a pilot program to open up WeChat Pay to foreigners. UnTour's Mr. Long, an American, was initially excited about the program. As of Friday, he'd had no success making his Visa or Mastercard work.

Tencent, which called lack of access to mobile payments a "major pain point" for foreigners, said the rollout is initially limited to certain situations, such as booking train tickets on a travel site.

The site is only available in Chinese.

Travelers have had more luck on Alipay, which introduced a seven-step process last week that requires visitors to submit passport and visa information to Alipay, before loading money using an overseas card onto a prepaid card.

In a bathroom near the Great Wall recently, Catherine De Witte, a Belgian marketing consultant, was getting frustrated. She waved her hands in front of a high-tech toilet-paper dispenser, jammed her fingers into the slot and finally pounded on the machine. She wasn't amused when she saw the QR code.

"You really need the restroom, and the restroom only gives you toilet paper if you can do something strange with your phone," she fumed.

Liao Yuxing, chief executive of the toilet-paper-dispenser maker Yunzhi Zhilian Network Technology Co., defends the preoccupation with QR codes as "a unique Chinese specialty."

"Just like we go to Japan to enjoy their culture, foreigners can experience Chinese culture by scanning codes," he said, suggesting the machines could act as conversation starters. "If you don't know how to scan this, ask a Chinese person," he said.

Ms. De Witte was in no mood for a cross-cultural chat. Her quandary was finally solved when a Chinese visitor whipped out a phone and handed over a few squares of paper.

--Yin Yijun contributed to this article.

Write to Shan Li at shan.li@wsj.com