diff --git a/.changeset/payment-option-empty-fields.md b/.changeset/payment-option-empty-fields.md
new file mode 100644
index 0000000..ca60103
--- /dev/null
+++ b/.changeset/payment-option-empty-fields.md
@@ -0,0 +1,10 @@
+---
+"@agentcommercekit/ack-pay": patch
+---
+
+Reject empty payment request and payment option identifiers.
+
+`paymentOptionSchema` accepted empty strings for `id`, `currency`, and
+`recipient`, and `paymentRequestSchema` accepted an empty request `id`, even
+though other fields such as `amount` already reject invalid values. Require a
+non-empty string for these fields in both the valibot and zod schemas.
diff --git a/packages/ack-pay/src/schemas/payment-option.test.ts b/packages/ack-pay/src/schemas/payment-option.test.ts
index 166b449..cfe3105 100644
--- a/packages/ack-pay/src/schemas/payment-option.test.ts
+++ b/packages/ack-pay/src/schemas/payment-option.test.ts
@@ -35,3 +35,24 @@ describe("paymentOptionSchema amount", () => {
     },
   )
 })
+
+describe.each([
+  [
+    "valibot",
+    (input: unknown) => v.safeParse(valibotPaymentOptionSchema, input).success,
+  ],
+  ["zod", (input: unknown) => zodPaymentOptionSchema.safeParse(input).success],
+] as const)("%s paymentOptionSchema empty fields", (_, accepts) => {
+  it.each(["id", "currency", "recipient"] as const)(
+    "rejects a payment option with an empty %s",
+    (field) => {
+      expect(
+        accepts({
+          ...paymentOption,
+          amount: 1,
+          [field]: "",
+        }),
+      ).toBe(false)
+    },
+  )
+})
diff --git a/packages/ack-pay/src/schemas/schemas.test.ts b/packages/ack-pay/src/schemas/schemas.test.ts
index 735b3ea..3359d83 100644
--- a/packages/ack-pay/src/schemas/schemas.test.ts
+++ b/packages/ack-pay/src/schemas/schemas.test.ts
@@ -17,6 +17,26 @@ const paymentRequest = {
   ],
 }
 
+const validators = {
+  valibot: (input: unknown) =>
+    v.safeParse(valibotPaymentRequestSchema, input).success,
+  zod: (input: unknown) => zodPaymentRequestSchema.safeParse(input).success,
+} as const
+
+describe.each(Object.entries(validators))(
+  "%s paymentRequestSchema",
+  (_, accepts) => {
+    it("rejects a payment request with an empty id", () => {
+      expect(
+        accepts({
+          ...paymentRequest,
+          id: "",
+        }),
+      ).toBe(false)
+    })
+  },
+)
+
 describe("paymentRequestSchema", () => {
   it("rejects invalid expiresAt strings instead of throwing", () => {
     const input = {
diff --git a/packages/ack-pay/src/schemas/valibot.ts b/packages/ack-pay/src/schemas/valibot.ts
index 75fc980..392b67f 100644
--- a/packages/ack-pay/src/schemas/valibot.ts
+++ b/packages/ack-pay/src/schemas/valibot.ts
@@ -5,6 +5,8 @@ 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()]),
   v.check((input) => !Number.isNaN(new Date(input).getTime()), "Invalid date"),
@@ -12,21 +14,21 @@ const timestampSchema = v.pipe(
 )
 
 export const paymentOptionSchema = v.object({
-  id: v.string(),
+  id: nonEmptyString,
   amount: v.union([
     v.pipe(v.number(), v.integer(), v.gtValue(0)),
     positiveIntegerString,
   ]),
   decimals: v.pipe(v.number(), v.integer(), v.toMinValue(0)),
-  currency: v.string(),
-  recipient: v.string(),
+  currency: nonEmptyString,
+  recipient: nonEmptyString,
   network: v.optional(v.string()),
   paymentService: v.optional(urlOrDidUri),
   receiptService: v.optional(urlOrDidUri),
 })
 
 export const paymentRequestSchema = v.object({
-  id: v.string(),
+  id: nonEmptyString,
   description: v.optional(v.string()),
   serviceCallback: v.optional(v.pipe(v.string(), v.url())),
   expiresAt: v.optional(timestampSchema),
diff --git a/packages/ack-pay/src/schemas/zod.ts b/packages/ack-pay/src/schemas/zod.ts
index 05cfdca..6a53974 100644
--- a/packages/ack-pay/src/schemas/zod.ts
+++ b/packages/ack-pay/src/schemas/zod.ts
@@ -5,6 +5,8 @@ import * as z from "zod"
 const urlOrDidUri = z.union([z.url(), didUriSchema])
 const positiveIntegerString = z.string().regex(/^[1-9]\d*$/)
 
+const nonEmptyString = z.string().min(1)
+
 const timestampSchema = z
   .union([z.date(), z.string()])
   .transform((val, ctx) => {
@@ -22,18 +24,18 @@ const timestampSchema = z
   })
 
 export const paymentOptionSchema = z.object({
-  id: z.string(),
+  id: nonEmptyString,
   amount: z.union([z.number().int().positive(), positiveIntegerString]),
   decimals: z.number().int().nonnegative(),
-  currency: z.string(),
-  recipient: z.string(),
+  currency: nonEmptyString,
+  recipient: nonEmptyString,
   network: z.string().optional(),
   paymentService: urlOrDidUri.optional(),
   receiptService: urlOrDidUri.optional(),
 })
 
 export const paymentRequestSchema = z.object({
-  id: z.string(),
+  id: nonEmptyString,
   description: z.string().optional(),
   serviceCallback: z.url().optional(),
   expiresAt: timestampSchema.optional(),