Shein’s IPO is being pitched at under $30 billion. Four years ago it was worth $100 billion.

Shein’s advisers are pitching the fast-fashion giant to investors at a valuation below $30 billion for its Hong Kong IPO, a roughly 70% drop from the $100 billion-plus valuation it hit in a 2022 private fundraising. Internally, Shein set a target of...