I would start with Geyser (https://geyser.fund/) to get them familiar with how payments work but the real magic with Geyser is that its free to join, no monthly fees (you only pay 4% when you receive a payment), payments go directly to their wallet, and you can even market it with affiliate links.

I think a lot of people are sleeping on Geyser. It's truly one of the most powerful bitcoin tools out there.