Add the desired Steam ID in the Server Console (Not in the Client)
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Access flags:
a - immunity (immune to AMX commands such as kick, slap, or ban.)
b - reservation (can join on reserved slots)
c - amx_kick command
d - amx_ban and amx_unban commands
e - amx_slay and amx_slap commands
f - amx_map command
g - amx_cvar command (not all cvars will be available)
h - amx_cfg command
i - amx_chat and other chat commands
j - amx_vote and other vote commands
k - access to sv_password cvar (by amx_cvar command)
l - access to amx_rcon command and rcon_password cvar (by amx_cvar command)
m - custom level A (for additional plugins)
n - custom level B
o - custom level C
p - custom level D
q - custom level E
r - custom level F
s - custom level G
t - custom level H
u - menu access
z - user
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Account flags:
a - disconnect player on invalid password
b - clan tag
c - this is steamid (or wonid)
d - this is ip
e - password is not checked (only name/ip/steamid needed)
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Example"STEAM_0:1:12345" "abcdefghijklmnopqrstu" "ce"
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Here is the deal, put your/the person's Steam ID (to check just type "Status" in the console"). Next, put what level you want the admin to be at (a-z) or what you care to do, then put the Account flags.
Steam ID is the easiest one and you don't really need a password.
It logs you in from your/that person's account only.
Test this by typing "amxmodmenu" in the console and see if admin privileges pop up.
If not, go to http://amxmod.net/doc/?p=amxusers for more info.