Vinted users have been reacting angrily following a change that caused items being listed as the wrong size.
The second-hand shopping app has updated its sizing categories for female and kids' apparel without notifying all shoppers about the modification.
Countless users and merchants have taken to social media saying Vinted listings now show a different size category compared to what was initially listed because of the remapping.
Vinted explained the updated approach better aligns with comparable marketplaces.
It has advised users to review their products and adjust the sizing manually where appropriate, which has left users frustrated.
Before the change, the sizes had both one number and one letter, like S/8 or M/10.
The updated approach includes a letter and a range like S/UK 8-10.
For certain items, the measurements have been reclassified - such as a large size was previously a 12 but is now a UK 16-18.
A fashion influencer, who produces content about larger sizing, said the change "makes both selling and buying harder".
"Few clothing companies classify XL as 20-22," as the platform currently indicates.
A different member, based in Glasgow, explained products she uploaded on Vinted with size 14 labels were showing in the marketplace as larger sizing 20-22.
"If anyone [who is] size 20-22 buys them they will likely be quite upset," she said.
Another shopper, based in Derby, stated she felt frustrated due to the update requiring manual adjustment the sizing for "all her products".
"This situation is especially annoying, because of my ongoing medical condition and Vinted sales have been crucial after experiencing income reduction," she explained.
The app has more than 100 million users, with 18 million British users.
It has become a favored option versus similar marketplaces including eBay and Depop.
This is not the initial instance when a surprising modification within the service has received backlash: last year, Vinted reversed a change concerning shipment methods following member complaints.