Shoppers are voicing their frustration following a change that caused listings displaying inaccurate size information.
The second-hand shopping app has updated its sizing categories for female and kids' apparel but did not contact all users about the change.
Countless users and merchants are posting online claiming that product pages now present a different size category than originally posted because of the remapping.
Vinted explained the updated approach better aligns with other platforms.
It has advised users to review their products and adjust the sizing manually where appropriate, which has left users frustrated.
Before the change, the sizing featured one number and one letter, for instance S/8 or M/10.
The new system has an alphabetical indicator and numerical range for example S/UK 8-10.
In some cases, the sizing has been recategorised - for example a size L used to be a 12 but currently displays as UK 16-18.
Frankie Bridger, who creates plus-size fashion videos, stated the update "complicates both purchasing and selling".
"Not many brands say XL is a 20-22," as the platform currently indicates.
Stephanie Gallen, based in Glasgow, explained products she uploaded featuring size 14 markings were displaying on the service as larger sizing 20-22.
"If anyone [who is] size 20-22 buys them they may become frustrated," she explained.
Another shopper, located in England, said she had been left angered by the change as she had to manually change the sizing for "all her products".
"Personally, this is quite irritating, because of my ongoing medical condition and selling on Vinted has been paramount for me since losing part of my income," she said.
The service features exceeding 100 million users, comprising 18 million UK members.
It has proved a popular alternative compared to resale services such as eBay and Depop.
This isn't the first time where an unanticipated change within the service has received backlash: previously, Vinted reversed a change concerning shipment methods following member complaints.
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