When placing orders on SMM panels, one of the main problems is that the number of likes, views, subscribers, etc. it can drop too quickly. Since there are different providers, and it is very difficult to guarantee a 0% drop, a feature called "replenishment" was invented to keep customers happy with the services they order, no matter what.
Some social media platforms update every few weeks or months to remove accounts that are no longer active. Because of this, drops happen. The refill feature means that your account will be refilled for free if there is a drop in followers, likes, opinions, etc. within a specified period of time.