Why is the Biden campaign trying to raise $100M four days before the election?

"Hey, it's Pete Buttigieg. This is the last time I'll text you for Joe and Kamala before Election Day. I know that they will restore competence, decency, and integrity to the Oval Office. But we have to make sure they win first. That's why the campaign's goal of raising $100M in these final days of October and $5.2M more of it through texts like these is so vital. Will you please donate $12 now to make sure we don't fall short? http://m.txtjoe.co/n8/7s2uic"