Shoppers are voicing their frustration due to a modification that led to items being listed as the wrong size.
The popular resale platform has revised its size classifications for female and kids' apparel without notifying every member regarding the update.
Many shoppers and sellers have taken to social media saying Vinted listings now show an altered size classification compared to what was initially listed because of the remapping.
The platform stated the revised method more closely matches similar services.
It has advised users to check their listings and manually change the size if necessary, resulting in member annoyance.
Previously, the sizes had both a single numeric size and a letter, such as S/8 or M/10.
The updated approach includes an alphabetical indicator and numerical range for example S/UK 8-10.
With some products, the size labels have been reassigned - like an L measurement used to be a 12 but is now a UK 16-18.
Frankie Bridger, who produces content about larger sizing, said the change "makes both selling and buying harder".
"Not many brands say XL is a 20-22," which is what Vinted now does.
A different member, from Glasgow, explained products she uploaded with size 14 tags were appearing on the platform as measurements 20-22.
"If buyers measuring 20-22 acquire them they may become frustrated," she said.
A different user, located in England, explained she became annoyed due to the update requiring manual adjustment the sizing for "all her products".
"For me this is particularly frustrating, as I'm chronically ill and platform income has been essential for me since losing part of my income," she explained.
The app has more than 100 million members, comprising 18 million UK members.
It has emerged as a preferred choice compared to resale services such as eBay and Depop.
This is not the initial instance when a surprising modification to the app has proved unpopular: previously, the service retracted a modification to its shipping options due to shopper criticism.