I understand that when an artist gets signed to a recording label, that sometimes, the distributor and label offer a PROMO releases for the forthcoming full release.

Usually back in the day where I am from, a PROMO is a FREE COPY.
These days I notice PROMOS in stores being SOLD.

So I was wondering, if the label and distro agree to release 100 promos and the distro pays for the manufacturing of this white label promo, is the label entitled to get paid from the distributor for promos?

How does this promo release work?
If one hundred PROMOS are sold, who keeps the money and why?

Thanks.
JBZ