For Youtube, Facebook and Twitter: Yes, you can, and we recommend putting links in your caption to guide the audience to your offer.
For Instagram: No. Instagram does NOT parse links in captions, and does not have plans to start supporting this option any time soon. We recommend to include your @username in your caption, and putting a link into your bio section instead.
We also recommend for you to purchase shoutouts with bio link, those are available as a filter option on our browse page, and what that means is that influencers will put a link of your choice into THEIR profile along with your shoutout.