In the language of German securities supervision, that is enough to trigger a formal examination, and a formal examination is enough to spook a market that had not been expecting one.

The substance, as far as it has emerged, is unglamorous. The possible violation concerns a disclosure in the notes to the accounts relating to a transaction with a related party, tied to Zalando's acquisition of the fashion platform About You.

The question is not whether the deal happened or what it cost, but whether Zalando properly disclosed a related-party element of it in the footnotes. The drama, in other words, is in the small print.

Zalando's response was quick and deliberately deflating. The company said it was in close contact with BaFin and described the matter as “a purely formal issue, but one that is not material, in the notes disclosures.”

That phrasing is doing a lot of work. Material is the word that separates a footnote correction from a problem that touches the actual numbers, and Zalando is insisting this is the former. The company has said the review has no impact on its financial KPIs or performance.

The market's reaction was sharper than the disclosure seemed to warrant, which is its own kind of signal. Analyst Andrew Ross at Barclays noted that the review had produced an unhelpful headline while sticking to a base case that it is a solvable issue.

His caveat was the one that matters for the share price: until BaFin concludes, the review will hang over the stock as an overhang, the analyst's term for a known unknown that investors price in until it resolves.

The timing is unkind. The probe landed during a broader tech sell-off, with Nasdaq futures falling and European shares slipping on the same session, so Zalando's drop arrived in a market already in a selling mood.

A regulatory question about accounting is exactly the sort of headline that gets punished harder when sentiment is fragile than when it is calm.

The About You deal that sits underneath all this was a notable piece of European e-commerce consolidation, a bet that scale would help Zalando compete in a market where margins are thin and platform economics rule, the same logic visible across recent European tech deals, from Bending Spoons' Nasdaq listing to the financing manoeuvres of companies like Manus reworking their ownership.

Acquisitions of that size leave long disclosure trails, and BaFin's review is, for now, a question about one line in that trail.

BaFin's enforcement reviews carry weight in Germany partly because of where the regulator has been. The watchdog spent the years after the Wirecard collapse rebuilding its credibility on exactly this kind of work, scrutinising the disclosures listed companies would rather it skimmed.

That history cuts both ways for Zalando. It means the regulator is unlikely to drop a review quietly, but it also means a footnote disclosure is a long way from the fraud that prompted the overhaul. The market, on Friday, was pricing the association more than the facts.

What happens next is procedural. BaFin will complete its examination on its own timetable, and Zalando will keep saying the issue is formal until told otherwise. The share price will decide for itself which version to believe in the meantime.