Affirm has taken on a lot of debt funding as opposed to equity funding. Partly because they are in the business of issuing loans and paying equity for the loans would be silly for founders/investors/employees.

The total amount of money raised is probably < $100mm in pure equity, and the valuation is probably a favorable $800mm when fudging the numbers.

With a recent WSJ article citing that 43% of student loan borrowers are currently not paying back debt, and with Affirm largely trying to issue loans to that "millenial" market, we will see how this high risk lending plays out.