MeanMrMustard: They "render services" for the campaign, and invoice millions.
...and try to keep it as quiet as possible, so that it appears that they were supporting Harris with their time, instead of being bought as a political campaign prop. The cringiest may have been Oprah, who tried to split hairs by claiming that she was not paid personally. Her production company was paid $1 million to produce what amounted to a political ad dressed up as an interview-slash-party.
It's a bad look, when millionaires are taking additional millions to endorse a candidate. The sadder thing is that it probably would have been seen as a good investment if she had won. The crime here, in many people's eyes, is not that she wasted so much money; it's that she spent so much and lost.