I had this one in mind:

Third-party advertising and sponsorships are not allowed. You may not advertise or promote third-party products, services, or brands through Medium posts, publications, or newsletters. This includes images that indicate brand sponsorship in a post or newsletter, or as part of a publication name or logo.

But maybe it could fall into this category with the right disclaimer:

Affiliate links, such as links out to Amazon with an affiliate code, or any other link out where you will receive a commission or other value, are allowed in posts. However, per Federal Trade Commission law, you must disclose the inclusion of these links in your post. This can be a simple sentence in the footer. (for further guidance, see FTC Rules and Guides)