Usually, due to new reporting laws, apps will tell you when you need to fill in your information as a seller report. If you need to pay taxes, it is up to you to submit, report, and pay your HRMC self-assessment in time.
Article source: https://www.huffingtonpost.co.uk/entry/vinted-ebay-depop-tax-rules-uk_uk_6abe5f96e4b02a789b333a22