When integrating the Cloud Director Orchestrator plugin, and using the workflow to create an OrgVCD object, the allocation models for 'Flex' is not available and is noticed in GUI :
For Example:
VMware Cloud Director 10.6
Support Limitation of the Plugin
Recommendation's are to use AllocationPool ( more contention and more reservations ) , or Pay-as-you-go (has a lower CPU , MEM requirement, which can help with resource contention)
NOTE: The only supported options are Pay-as-you-go, Allocation, and Reservation models