Another easy way to find which interface number to use is by running the lsusb command (with recommended -d vendorid/productid switch) on a Linux box or VM - it will print out all interface numbers for each interface in a nice output. The lsusb on macOS isn’t the same, and shows a lot less detail, so I recommend the Linux version. You only have to do this once, as the interface numbers won’t change on a particular USB device. Usually the interface numbers are 0 or 1, so you could also just guess and check.