The available purchase models are:
PAYG doesn’t require any commitment and is billed in arrears. Monthly Flex credits are consumed at a lower rate than PAYG for PaaS, and at the same rate for IaaS.
Additionally, Monthly Flex credits expire each month. The minimum term for Monthly Flex is 12 months, so each month 1/12th of the credits need to be used by the customer or they are forfeited for that month.