Fixed all 31 errors on /platform/administration/ai/ page. (1) inc_ai_manager.php — $_GET[page] undefined, added ?? fallback. (2) billing.php — 26 undefined variables when no ?id= parameter (creditlimit, hasBilling, isPayer, chat_setting, alerts, ais, allow_memory, balance_color, balance_percentage, usage, total_cost, total_tokens, remaining_balance, overall_* vars). Added default initializations before the if(isset($_GET[id])) block. Fixed $_GET[host] with ?? fallback (3 occurrences). Fixed $inChargeArray[$chat_setting[payer]] double undefined key. (3) settings_js.php — $_GET[id] without ?? fallback (2 occurrences), $ais and $alerts undefined. All 3 caused a JS SyntaxError from malformed PHP output. Result: 31 errors → 0 errors.