[Estland]

Use something like:

#include <amxmodx>

new const g_szServerIP[] = "IP:PORT";

public plugin_init() 
{
    new szIP[20];
    get_user_ip(0, szIP, charsmax(szIP), false);
    
    if( !equal(szIP, g_szServerIP) )
    {
        set_fail_state("This plugin is protected!");
    }
}