Your payment is set by the terms and conditions of your loan agreement and is a function of your authorized purchases. Your loan agreement provides you with an estimated repayment schedule that includes the amount of each monthly payment based on full utilization of your credit limit. Keep in mind, however, you are only obligated for the actual payments you authorize to your contractor/merchant.
Each billing statement will identify the transactions on your account, the interest that is being billed to your account, the principal balance, and actual minimum monthly payment due for that billing cycle.