TL;DR: The Chinese government document 2018年支付体系运行总体情况 (linked in nwellnhof's comment) says:
2018年 ... 移动支付业务605.31亿笔，金额277.39万亿元 ...
In 2018 ... [there were] mobile payment services [of] 60.531 billion transactions, [and] monetary value 277.39 trillion yuan ...
First, some context.
Chinese people virtually don't pay in cash anymore, they pay using their phones, typically using WeChat (微信) and/or Alipay (支付宝). They also buy a lot online, using TaoBao (淘宝), JingDong (京东), etc.
It's almost like cash is obsolete here. This includes buying basically anything, e.g., you can buy a car, make everyday transactions, pay your rent, etc., using these services.
So, large numbers are unsurprising: it probably includes a billion people making a large proportion of their transactions this way.
My Chinese is not fantastic, but I'll attempt a translation of the relevant information in the Chinese government document linked in nwellnhof's comment:
4. Electronic payment
Mobile payment business rapidly increased in quantity. 2018 banking and finance dealt with electronic payments [by] 9 services [of] 175.192 billion transactions, [and] monetary value 2,539.70 trillion yuan. Among these, online payment business [of] 57,013 billion transactions, [and] monetary value 2,126.30 trillion yuan, [and] over this period, respective growth [of] 17.36% and 2.47%; mobile payment services [of] 60.531 billion transactions, [and] monetary value 277.39 trillion yuan, [and] over this period, respective growth [of] 61.19% and 36.69%; telephone payment service [of] 158 million translations, [and] monetary value 7.68 trillion yuan, [and] over this period a respective decline [of] 0.99% and 12.54%.
2018年支付体系运行总体情况 2018 Payment System Operation Overall Situation (pdf)
- 1 billion = 1,000 million = 1,000,000,000
- 100 million = 1亿
- 1 trillion = 1,000 billion = 1万亿