Henry Rousso is a French historian and one of the pre-eminent scholars of the Holocaust. He came to the USA in order to give a lecture, for which he was to be paid an honorarium of $2000. He held a tourist visa.
However, he was held for 10 hours by an agent who was apparently unaware that there are exceptions to the general rule that people in the USA on tourist visas cannot be paid. Honorariums for speeches at academic conferences are such an example.