Deliveroo IPO: Why are 7,000 customers barred from trading for a week?

Charged £3.90 a share, a fall of 28 per cent in the share price since then has wiped £14million off the initial £50million of shares which had been offered to a select group of customers. https://www.dailymail.co.uk/money/investing/article-9427111/Deliveroo-IPO-7-000-customers-barred-trading-week.html?ns_mchannel=rss&ns_campaign=1490&ito=1490