google says it can't find a single reference to "addban" anywhere on tixati.com which I assume includes these forums.
all I can see is
on the Commands menu with no indication what said parameters might be.
When I try to guess something like an IP 188.8.131.52/32 it returns:
Invalid ban string. Press F1 for help.
Pressing F1 leads simply to the support pages which have nothing on this subject.