fix(chat): allow nullable credit fields

src/data/schemas/chat/chat_send_response.ts

@@ -3,7 +3,7 @@
  * 
  */
 import { z } from "zod";
-import { booleanOrFalse, stringOrNull } from "../nullable-defaults";
+import { booleanOrFalse, numberOrZero, stringOrNull } from "../nullable-defaults";
 import { ChatImageSchema, ChatLockDetailSchema } from "./chat_payloads";
 
 export const ChatSendResponseSchema = z.object({
@@ -17,10 +17,10 @@ export const ChatSendResponseSchema = z.object({
   lockDetail: ChatLockDetailSchema,
   canSendMessage: z.boolean().default(true),
   cannotSendReason: stringOrNull,
-  creditBalance: z.number().default(0),
-  creditsCharged: z.number().default(0),
-  requiredCredits: z.number().default(0),
-  shortfallCredits: z.number().default(0),
+  creditBalance: numberOrZero,
+  creditsCharged: numberOrZero,
+  requiredCredits: numberOrZero,
+  shortfallCredits: numberOrZero,
 });
 
 export type ChatSendResponseInput = z.input<typeof ChatSendResponseSchema>;