Using CONS port for serial IO

I’m out of serial IO on the cube pilot orange plus on the ADS-B carrier board and I’m trying to use the ‘CONS’ port to connect to a VOXL2. From the documentation, it looks like it’s UART7 and I would connect to /dev/ttyS4, I’m able to open the port but I cannot read/write to it. I’m based off of PX4 1.14. Any ideas?