I don't know what the law is. Years ago, but I've been paid for doing a focus group in cash. So there's presumably some threshold where you can just have essentially a petty cash business expense.

Obviously meals and so forth as well. (And, assuming the law hasn't changed, US government employees have to pay for even a modest meal at a company's executive briefing center.)

OTOH, I've had 1099s for even very modest side-consulting revenue.