There are no additional usage reporting procedures introduced with Flex model. Partners will continue to generate Usage Meter reports as you normally do, report the usage through Prism Portal and navigated to VMware Business Portal.
Usage Meter reports may continue to refer vCloud SP bundles which you are required to report against each SKU in VMware Business Portal. The VMware Business Portal backend system will automatically translate this usage submitted against each vCloud SP bundles to Flex. There are no specific additional steps required to submit usage for Flex.