This is because of how IPOs work:
In an IPO, the company (eg. Twilio) sells the issued shares to an underwriter (eg. JP Morgan) at an agreed amount (eg. $15) and then the underwriter turns around and sells those on the market for whatever people will pay for them (eg. $24).
If those first shares get bought for less than the offering price ($15) the company got a good deal on their shares and the underwriter loses money. If the shares get bought for more than the offering price, the company loses money and the underwriter profits.
This is one way underwriters make money, by being able to turn around and sell those shares to the public market for more than they bought them for.
Twilio issued $10m shares at $15 and the market opened up 60%, so they raised $150M and left $90M on the table.
10m shares * (24 - 15) $/share = $90M