a bitmask is always an integer, never a string. If register 100 is not a bitmask (which it doesn’t seem to be from your screenshot), then no idea, ask the vendor what a value of 8 might mean.
But be aware, that the register could be off by 1 in any direction. So in order to get the register 109 from your device, you might have to configure 108 or 110 to get the correct register (depending on how they start counting, with 0 or 1). All my modbus registers for E3DC are off by 1 (don’t recall in which direction), so maybe the same applies to your device. Other than that, config looks fine.
