diff --git a/.changeset/reject-empty-network.md b/.changeset/reject-empty-network.md
new file mode 100644
index 0000000..a07ca03
--- /dev/null
+++ b/.changeset/reject-empty-network.md
@@ -0,0 +1,5 @@
+---
+"@agentcommercekit/ack-pay": patch
+---
+
+Reject an empty `network` on payment options when the field is present.
diff --git a/packages/ack-pay/src/schemas/payment-option.test.ts b/packages/ack-pay/src/schemas/payment-option.test.ts
index 166b449..c76cef2 100644
--- a/packages/ack-pay/src/schemas/payment-option.test.ts
+++ b/packages/ack-pay/src/schemas/payment-option.test.ts
@@ -35,3 +35,40 @@ describe("paymentOptionSchema amount", () => {
     },
   )
 })
+
+describe.each([
+  [
+    "valibot",
+    (input: unknown) => v.safeParse(valibotPaymentOptionSchema, input).success,
+  ],
+  ["zod", (input: unknown) => zodPaymentOptionSchema.safeParse(input).success],
+] as const)("%s paymentOptionSchema network", (_, accepts) => {
+  it("accepts a payment option with network omitted", () => {
+    expect(
+      accepts({
+        ...paymentOption,
+        amount: 1,
+      }),
+    ).toBe(true)
+  })
+
+  it("accepts a payment option with a non-empty network", () => {
+    expect(
+      accepts({
+        ...paymentOption,
+        amount: 1,
+        network: "eip155:8453",
+      }),
+    ).toBe(true)
+  })
+
+  it("rejects a payment option with an empty network", () => {
+    expect(
+      accepts({
+        ...paymentOption,
+        amount: 1,
+        network: "",
+      }),
+    ).toBe(false)
+  })
+})
diff --git a/packages/ack-pay/src/schemas/valibot.ts b/packages/ack-pay/src/schemas/valibot.ts
index 75fc980..e7f96f4 100644
--- a/packages/ack-pay/src/schemas/valibot.ts
+++ b/packages/ack-pay/src/schemas/valibot.ts
@@ -4,6 +4,7 @@ import * as v from "valibot"
 
 const urlOrDidUri = v.union([v.pipe(v.string(), v.url()), didUriSchema])
 const positiveIntegerString = v.pipe(v.string(), v.regex(/^[1-9]\d*$/))
+const nonEmptyString = v.pipe(v.string(), v.minLength(1))
 
 const timestampSchema = v.pipe(
   v.union([v.date(), v.string()]),
@@ -20,7 +21,7 @@ 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(nonEmptyString),
   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(),
 })