What is the key element in the 'fifth form of marriage', according to the Manusmriti?

Groom's wealth and offerings to the bride

The Manusmriti describes various forms of marriage, including the first, fourth, fifth, and sixth, as follows:

First: A father gifts his daughter to a knowledgeable man proficient in the Vedas. He dresses her in costly attire, honors her with valuable jewels, and personally invites the groom.
Fourth: A father gifts his daughter to the groom after addressing the couple with the words, "May both of you perform your duties together," and showing honor to the groom.
Fifth: The groom receives the maiden after providing as much wealth as he can afford to the kinsmen and the bride herself, according to his own discretion.
Sixth: A voluntary union between a maiden and her lover, arising from mutual desire.