diff --git a/.changeset/reject-empty-payment-option-network.md b/.changeset/reject-empty-payment-option-network.md
new file mode 100644
index 0000000..c7e22ee
--- /dev/null
+++ b/.changeset/reject-empty-payment-option-network.md
@@ -0,0 +1,5 @@
+---
+"@agentcommercekit/ack-pay": patch
+---
+
+Reject empty-string `network` values on payment options while still allowing the field to be omitted.
diff --git a/packages/ack-pay/src/schemas/payment-option.test.ts b/packages/ack-pay/src/schemas/payment-option.test.ts
index 166b449..90a9ec3 100644
--- a/packages/ack-pay/src/schemas/payment-option.test.ts
+++ b/packages/ack-pay/src/schemas/payment-option.test.ts
@@ -35,3 +35,23 @@ describe("paymentOptionSchema amount", () => {
     },
   )
 })
+
+describe("paymentOptionSchema network", () => {
+  it("accepts omitted network", () => {
+    const value = { ...paymentOption, amount: 1 }
+    expect(v.safeParse(valibotPaymentOptionSchema, value).success).toBe(true)
+    expect(zodPaymentOptionSchema.safeParse(value).success).toBe(true)
+  })
+
+  it("accepts non-empty network", () => {
+    const value = { ...paymentOption, amount: 1, network: "eip155:84532" }
+    expect(v.safeParse(valibotPaymentOptionSchema, value).success).toBe(true)
+    expect(zodPaymentOptionSchema.safeParse(value).success).toBe(true)
+  })
+
+  it("rejects empty network", () => {
+    const value = { ...paymentOption, amount: 1, network: "" }
+    expect(v.safeParse(valibotPaymentOptionSchema, value).success).toBe(false)
+    expect(zodPaymentOptionSchema.safeParse(value).success).toBe(false)
+  })
+})
diff --git a/packages/ack-pay/src/schemas/valibot.ts b/packages/ack-pay/src/schemas/valibot.ts
index 75fc980..40c8666 100644
--- a/packages/ack-pay/src/schemas/valibot.ts
+++ b/packages/ack-pay/src/schemas/valibot.ts
@@ -20,7 +20,7 @@ export const paymentOptionSchema = v.object({
   decimals: v.pipe(v.number(), v.integer(), v.toMinValue(0)),
   currency: v.string(),
   recipient: v.string(),
-  network: v.optional(v.string()),
+  network: v.optional(v.pipe(v.string(), v.minLength(1))),
   paymentService: v.optional(urlOrDidUri),
   receiptService: v.optional(urlOrDidUri),
 })
diff --git a/packages/ack-pay/src/schemas/zod.ts b/packages/ack-pay/src/schemas/zod.ts
index 05cfdca..1a5e4fa 100644
--- a/packages/ack-pay/src/schemas/zod.ts
+++ b/packages/ack-pay/src/schemas/zod.ts
@@ -27,7 +27,7 @@ export const paymentOptionSchema = z.object({
   decimals: z.number().int().nonnegative(),
   currency: z.string(),
   recipient: z.string(),
-  network: z.string().optional(),
+  network: z.string().min(1).optional(),
   paymentService: urlOrDidUri.optional(),
   receiptService: urlOrDidUri.optional(),
 })