Vinted users have been reacting angrily following a change that caused items being listed as the wrong size.
This online marketplace has revised its measurement guidelines for women's and children's garments failing to inform all shoppers about the modification.
Numerous buyers and vendors are posting online saying Vinted listings now show a different size category than originally posted because of the remapping.
The company said the new system was more in line with similar services.
They have suggested members to check their listings and adjust the sizing manually where appropriate, which has left users frustrated.
Previously, the measurements included a single numeric size and a letter, like S/8 or M/10.
The updated approach includes an alphabetical indicator and numerical range such as S/UK 8-10.
In some cases, the sizing has been recategorised - such as a large size was formerly size 12 but is now a UK 16-18.
One content creator, who makes TikTok content about plus-size fashion, explained the modification "makes transactions more difficult".
"Few clothing companies classify XL as 20-22," the way the service now categorizes.
Another user, from Glasgow, explained products she uploaded on Vinted with size 14 labels were appearing on the platform as size 20–22.
"If anyone [who is] size 20-22 buys them they may become frustrated," she said.
Another shopper, located in England, stated she felt frustrated due to the update requiring manual adjustment the sizes on "every single listing".
"For me this is particularly frustrating, since I have chronic health issues and Vinted sales have been crucial following partial earnings loss," she explained.
The platform boasts over 100 million users, with 18 million British users.
It has emerged as a preferred choice to second-hand platforms like eBay and Depop.
This isn't the first time when a surprising modification to the app has proved unpopular: last year, the platform withdrew an update concerning shipment methods following member complaints.
A tech journalist specializing in UK digital policy and startup ecosystems, with a background in computer science.