The only time I have heard of that is when sponsors buy a slot to pitch their product or service. Was that your situation?

In most conferences that are not marketing-oriented, the speakers are the product being sold to the attendees. Many conferences pay the speaker's expenses for travel, and may even pay them some speaking fee.

If you are a speaker being offered a fee to speak, however, be very careful about overseas conferences. People have been turned away at the border because the officials may see the money being paid as a job.