How is the max share price used by the broker when a customer indicates their interest for an IPO?

Some brokers allow their customers to specify a max share price when indicate interest for an IPO. Examples of such brokers: Robinhood and E-Trade. Examples of brokers who don't let customers specify a max share price: Charles Schwab and Fidelity (or maybe that depends on the IPO?).

How is the max share price used by the broker when a customer indicates their interest for an IPO?