Hello Brian,
You also need to enable the MCR.IRMQ bit to enable the Individual Mask.


In the SDK, the example flexcan_loopback, the FLEXCAN_GetDefaultConfig saves the configuration values in the structure, you need to change it to flexcanConfig.enableIndividMask = true and after that call the next API:
FLEXCAN_SetRxIndividualMask(CAN_Type *base, uint8_t maskIdx, uint32_t mask)
I hope this helps you.
Best Regards,
Alexis Andalon