Using MC version 1.10.2 and mod version 1.3.1.

Thanks you for letting me know of this issue. Have you tried doing 6410:0 or 6410 as just the id. Could you put a screenshot of the add gui with no text inputed? I've not used the mod in a while for that version.

Going to close this because I'm pretty sure the issue is with the / and not the mod it's self