When selling items, there are certain limitations and restrictions effective in order to ensure Creator activity. Creator requirements for selling items are updated based on sales from the past 30 days. So, if you’ve sold fewer items recently, you'll need to sell more to meet the monthly requirement. The number of sales you have may suddenly decrease if it's been over 30 days since those sales were originally counted, and they're no longer included in the current tally due to time having passed.