UMC 1820 and UAD Apollo 2 ADAT not working

Help! I cant get my UMC1820 to talk to my apollo over ADAT. My understanding is this should be very simple and straightforward however there is no good procedures online for this. I need help fast. Each item (UAD and UMC) work fine individually so there is no fault with the devices nor is there an issue with the optic cable as I have tested several.