While you can use third-party services like Fiverr to buy Medium followers, doing so is generally discouraged. Most "bought" followers are inactive accounts or bots that do not read your work, meaning they won't help you earn money through the Medium Partner Program, which relies on actual reading time from paid members.
Instead of buying followers, most successful writers recommend organic growth strategies: How to Grow Organically buy medium followers
: Join established Medium Publications related to your niche. This places your work in front of an existing audience. While you can use third-party services like Fiverr