Code:
server_cmd("banid 30 #%d", get_user_userid(id))
replace that with
Code:
new authid[35]
get_user_authid(id,authid,34)
server_cmd("amx_ban 30 %s 70 kills", authid)
As amxbans is SQL based u want to either use the amx_ban command the system gives u OR u wanna write an entire function for it which will make a SQL connection to the database and then add it. But this SHOULD work.