@Adam J - thanks!
Create incentives for their audience. So send them a 10% off coupon code for their followers with the package, this way they have a reason to post and their followers have a reason to buy.
Follow up can be simple.
"Hey {name}, hope you received {product} - what do you think about {something specific}?
PS: I also sent in a coupon code for your followers, don't forget to add it in case you share {brand} on your insta"
This {something specific} can be your USP, something they can share on their socials so it sparks ideas too.