diff --git a/changelog.d/fixes/provider-node-null-quota-reset.md b/changelog.d/fixes/provider-node-null-quota-reset.md
new file mode 100644
index 0000000000..a8bdd9aeae
--- /dev/null
+++ b/changelog.d/fixes/provider-node-null-quota-reset.md
@@ -0,0 +1 @@
+- **fix(validation):** Provider node edits no longer fail with a generic "Invalid request" when the optional daily-quota reset fields are left blank. The dashboard sends `dailyQuotaResetTimezone` and `dailyQuotaResetHour` as `null`, and only the hour accepted it. ([#13066](https://github.com/diegosouzapw/OmniRoute/issues/13066))
diff --git a/src/shared/validation/schemas/provider.ts b/src/shared/validation/schemas/provider.ts
index 5d845f1653..e6f324891b 100644
--- a/src/shared/validation/schemas/provider.ts
+++ b/src/shared/validation/schemas/provider.ts
@@ -35,10 +35,17 @@ import { isValidProviderIconUrl } from "@/shared/validation/iconUrl";
 
 export { validateProviderSpecificData };
 
+// Nullable as well as optional, to match dailyQuotaResetHourSchema below. The
+// dashboard sends both fields as null when they are left blank, and the two
+// schemas disagreeing about that meant an edit touching neither of them still
+// failed validation on this one (#13066). The storage layer already coerces to
+// null (`data.dailyQuotaResetTimezone || null` in db/providers/nodes.ts), so
+// accepting null here changes nothing downstream.
 const dailyQuotaResetTimezoneSchema = z
   .string()
   .trim()
   .optional()
+  .nullable()
   .or(z.literal(""))
   .refine((value) => !value || isValidIanaTimeZone(value), {
     message: "Unknown IANA timezone",
@@ -519,9 +526,7 @@ export const updateProviderConnectionSchema = z
     errorCode: z.union([z.string(), z.null()]).optional(),
     rateLimitedUntil: z.union([z.string(), z.null()]).optional(),
     lastTested: z.union([z.string(), z.null()]).optional(),
-    healthCheckInterval: z
-      .union([z.null(), z.coerce.number().int().min(0).max(1440)])
-      .optional(),
+    healthCheckInterval: z.union([z.null(), z.coerce.number().int().min(0).max(1440)]).optional(),
     group: z.union([z.string().max(100), z.null()]).optional(),
     maxConcurrent: z.union([z.null(), z.coerce.number().int().min(0)]).optional(),
     // Per-window quota cutoffs. Map keys are window names (e.g. "window5h",
diff --git a/tests/unit/provider-node-null-quota-reset-13066.test.ts b/tests/unit/provider-node-null-quota-reset-13066.test.ts
new file mode 100644
index 0000000000..75e931a7c3
--- /dev/null
+++ b/tests/unit/provider-node-null-quota-reset-13066.test.ts
@@ -0,0 +1,89 @@
+import test from "node:test";
+import assert from "node:assert/strict";
+import {
+  createProviderNodeSchema,
+  updateProviderNodeSchema,
+} from "../../src/shared/validation/schemas/provider.ts";
+
+// Regression for #13066: saving an edit to a custom OpenAI-compatible node failed
+// with a generic "Invalid request" whenever the optional daily-quota reset fields
+// were left blank. The dashboard sends both as `null`, and the two schemas
+// disagreed about that: `dailyQuotaResetHour` was `.optional().nullable()`, while
+// `dailyQuotaResetTimezone` was only `.optional()`. So `null` passed for the hour
+// and was rejected for the timezone, and the whole PUT 400'd on a field the user
+// had not touched. The failure surfaced while changing the API type, which made
+// it look as though changing the API type was broken.
+//
+// The storage layer has always coerced these to null (`data.dailyQuotaResetTimezone
+// || null` in db/providers/nodes.ts), so accepting null costs nothing downstream.
+
+const base = {
+  name: "My node",
+  prefix: "mynode",
+  apiType: "chat" as const,
+  baseUrl: "https://example.invalid/v1",
+};
+
+test("update accepts a null timezone alongside a null hour (#13066)", () => {
+  const result = updateProviderNodeSchema.safeParse({
+    ...base,
+    dailyQuotaResetTimezone: null,
+    dailyQuotaResetHour: null,
+  });
+  assert.equal(result.success, true, JSON.stringify(result.error?.issues));
+});
+
+test("create accepts the same null pair (#13066)", () => {
+  const result = createProviderNodeSchema.safeParse({
+    ...base,
+    dailyQuotaResetTimezone: null,
+    dailyQuotaResetHour: null,
+  });
+  assert.equal(result.success, true, JSON.stringify(result.error?.issues));
+});
+
+test("a null timezone is accepted on its own, not only beside a null hour", () => {
+  // The two fields are independent; the pairing above is just what the dashboard
+  // happens to send. A fix that only tolerated the pair would still reject this.
+  const result = updateProviderNodeSchema.safeParse({
+    ...base,
+    dailyQuotaResetTimezone: null,
+    dailyQuotaResetHour: 3,
+  });
+  assert.equal(result.success, true, JSON.stringify(result.error?.issues));
+});
+
+test("the fields stay optional and blank-string still passes", () => {
+  assert.equal(updateProviderNodeSchema.safeParse({ ...base }).success, true);
+  assert.equal(
+    updateProviderNodeSchema.safeParse({ ...base, dailyQuotaResetTimezone: "" }).success,
+    true
+  );
+});
+
+test("a real timezone still round-trips", () => {
+  const result = updateProviderNodeSchema.safeParse({
+    ...base,
+    dailyQuotaResetTimezone: "Asia/Ho_Chi_Minh",
+    dailyQuotaResetHour: 0,
+  });
+  assert.equal(result.success, true, JSON.stringify(result.error?.issues));
+});
+
+test("an unknown timezone is still rejected", () => {
+  // Accepting null must not widen the field into accepting anything: the IANA
+  // check is the reason this schema exists.
+  const result = updateProviderNodeSchema.safeParse({
+    ...base,
+    dailyQuotaResetTimezone: "Mars/Olympus_Mons",
+  });
+  assert.equal(result.success, false);
+});
+
+test("an out-of-range hour is still rejected", () => {
+  const result = updateProviderNodeSchema.safeParse({
+    ...base,
+    dailyQuotaResetHour: 24,
+  });
+  assert.equal(result.success, false);
+});