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 women's and children's garments but did not contact all shoppers about the modification.
Countless users and merchants are posting online claiming that product pages now present a different size category than originally posted as a result of the reclassification.
The platform stated the new system was more in line with comparable marketplaces.
It has advised users to review their products and adjust the sizing manually if necessary, which has left users frustrated.
Before the change, the sizes had both numerical and alphabetical indicators, such as S/8 or M/10.
The revised method features a letter with a size spectrum such as S/UK 8-10.
In some cases, the measurements have been reclassified - such as a large size used to be a 12 but now shows as UK 16-18.
Frankie Bridger, who makes TikTok content about plus-size fashion, said the change "makes both selling and buying harder".
"Not many brands say XL is a 20-22," the way the service now categorizes.
Stephanie Gallen, located in Scotland, explained products she uploaded with size 14 tags were appearing on the platform as larger sizing 20-22.
"If buyers measuring 20-22 acquire them they may become frustrated," she explained.
A different user, from Derby, stated she felt frustrated by the change as she had to manually change the sizes on "every single listing".
"For me this is particularly frustrating, since I have chronic health issues and selling on Vinted has been paramount after experiencing income reduction," she explained.
The app has more than 100 million members, 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: last year, the service retracted a modification to its shipping options after backlash from users.