When does my request volume (monthly API credit) reset?

Your call credit replenishes on the 1st day of each month, no matter when your billing cycle begins. 

In simpler terms, if you start your first month’s subscription on the 20th, you’ll still receive your full request quota for that initial month. When the next month begins, your call credits will reset on the 1st day, and you’ll be allocated your full request quota again.