When does circle charge the credit card on file for credit refills

Today I ran out of credits on my circleci account which meant my entire pipeline stopped. I have yet to be charged to refill it and there is no way to refill it in the dashboard of my account. How do I prevent my account from running out of credits or get circle to charge my credit card again. It seems that up till now I’ve never not had credits in my account.

Thanks!