Shoppers are voicing their frustration following a change that caused listings displaying inaccurate size information.
The popular resale platform has updated its sizing categories for women's and children's garments but did not contact all users about the change.
Many shoppers and sellers have taken to social media saying Vinted listings now show a different size category than originally posted due to the recalibration.
The company said the new system was more in line with comparable marketplaces.
They have suggested members to review their products and adjust the sizing manually if necessary, causing user dissatisfaction.
Earlier, the sizes had both numerical and alphabetical indicators, like S/8 or M/10.
The revised method features a letter and a range for example S/UK 8-10.
In some cases, the sizing has been recategorised - like an L measurement was formerly size 12 but currently displays as UK 16-18.
A fashion influencer, who creates plus-size fashion videos, explained the modification "makes transactions more difficult".
"Few clothing companies classify XL as 20-22," the way the service now categorizes.
Stephanie Gallen, located in Scotland, said garments she listed on Vinted with size 14 labels were appearing on the platform as measurements 20-22.
"Should someone sized 20-22 purchase these they may become frustrated," she explained.
A different user, based in Derby, said she had been left angered due to the update requiring manual adjustment the measurements for "each individual item".
"This situation is especially annoying, since I have chronic health issues and platform income has been essential following partial earnings loss," she explained.
The platform boasts over 100 million users, including 18 million in the UK.
It has become a favored option compared to resale services such as eBay and Depop.
This represents another occasion that an unexpected update to the app has proved unpopular: last year, the service retracted a modification regarding delivery choices due to shopper criticism.
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