diff --git a/lib/db/db-client.ts b/lib/db/db-client.ts
index e525e65..9751c48 100644
--- a/lib/db/db-client.ts
+++ b/lib/db/db-client.ts
@@ -2,7 +2,13 @@ import { createStore, type StoreApi } from "zustand/vanilla"
 import { immer } from "zustand/middleware/immer"
 import { hoist, type HoistedStoreApi } from "zustand-hoist"
 
-import { databaseSchema, type DatabaseSchema, type Thing } from "./schema.ts"
+import {
+  databaseSchema,
+  type DatabaseSchema,
+  type Payment,
+  type PaymentStatus,
+  type Thing,
+} from "./schema.ts"
 import { combine } from "zustand/middleware"
 
 export const createDatabase = () => {
@@ -11,7 +17,14 @@ export const createDatabase = () => {
 
 export type DbClient = ReturnType<typeof createDatabase>
 
-const initializer = combine(databaseSchema.parse({}), (set) => ({
+type AddPaymentInput = Omit<
+  Payment,
+  "payment_id" | "status" | "created_at" | "updated_at"
+> & {
+  status?: PaymentStatus
+}
+
+const initializer = combine(databaseSchema.parse({}), (set, get) => ({
   addThing: (thing: Omit<Thing, "thing_id">) => {
     set((state) => ({
       things: [
@@ -21,4 +34,65 @@ const initializer = combine(databaseSchema.parse({}), (set) => ({
       idCounter: state.idCounter + 1,
     }))
   },
+
+  /**
+   * Create a new payment. If an `idempotency_key` is provided and a payment
+   * already exists with that key, that existing payment is returned without
+   * creating a duplicate — this lets clients retry sends safely.
+   */
+  addPayment: (input: AddPaymentInput): Payment => {
+    if (input.idempotency_key) {
+      const existing = get().payments.find(
+        (p) => p.idempotency_key === input.idempotency_key,
+      )
+      if (existing) return existing
+    }
+    const now = new Date().toISOString()
+    const state = get()
+    const payment: Payment = {
+      payment_id: state.paymentIdCounter.toString(),
+      recipient: input.recipient,
+      amount: input.amount,
+      currency: input.currency ?? "USD",
+      status: input.status ?? "pending",
+      bounty_id: input.bounty_id ?? null,
+      issue_number: input.issue_number ?? null,
+      repository: input.repository ?? null,
+      idempotency_key: input.idempotency_key ?? null,
+      created_at: now,
+      updated_at: now,
+    }
+    set((s) => ({
+      payments: [...s.payments, payment],
+      paymentIdCounter: s.paymentIdCounter + 1,
+    }))
+    return payment
+  },
+
+  /**
+   * Transition a payment to a new status (e.g. "completed" or "canceled").
+   * Refuses to mutate payments already in a terminal state — this mirrors
+   * how real payment processors guard against retroactive edits.
+   */
+  updatePaymentStatus: (payment_id: string, status: PaymentStatus): Payment | null => {
+    const state = get()
+    const target = state.payments.find((p) => p.payment_id === payment_id)
+    if (!target) return null
+    if (target.status === "completed" || target.status === "canceled") {
+      // Terminal — return unchanged to keep history immutable.
+      return target
+    }
+    const now = new Date().toISOString()
+    const updated: Payment = { ...target, status, updated_at: now }
+    set((s) => ({
+      payments: s.payments.map((p) =>
+        p.payment_id === payment_id ? updated : p,
+      ),
+    }))
+    return updated
+  },
+
+  getPayment: (payment_id: string): Payment | null => {
+    return get().payments.find((p) => p.payment_id === payment_id) ?? null
+  },
 }))
diff --git a/lib/db/schema.ts b/lib/db/schema.ts
index 8377516..b65708c 100644
--- a/lib/db/schema.ts
+++ b/lib/db/schema.ts
@@ -9,8 +9,33 @@ export const thingSchema = z.object({
 })
 export type Thing = z.infer<typeof thingSchema>
 
+export const paymentStatusEnum = z.enum([
+  "pending",
+  "completed",
+  "canceled",
+  "failed",
+])
+export type PaymentStatus = z.infer<typeof paymentStatusEnum>
+
+export const paymentSchema = z.object({
+  payment_id: z.string(),
+  recipient: z.string(),
+  amount: z.number(),
+  currency: z.string().default("USD"),
+  status: paymentStatusEnum.default("pending"),
+  bounty_id: z.string().nullable().default(null),
+  issue_number: z.number().nullable().default(null),
+  repository: z.string().nullable().default(null),
+  idempotency_key: z.string().nullable().default(null),
+  created_at: z.string(),
+  updated_at: z.string(),
+})
+export type Payment = z.infer<typeof paymentSchema>
+
 export const databaseSchema = z.object({
   idCounter: z.number().default(0),
   things: z.array(thingSchema).default([]),
+  paymentIdCounter: z.number().default(0),
+  payments: z.array(paymentSchema).default([]),
 })
 export type DatabaseSchema = z.infer<typeof databaseSchema>
diff --git a/routes/payments/cancel.ts b/routes/payments/cancel.ts
new file mode 100644
index 0000000..0d9d8b0
--- /dev/null
+++ b/routes/payments/cancel.ts
@@ -0,0 +1,24 @@
+import { withRouteSpec } from "lib/middleware/with-winter-spec"
+import { z } from "zod"
+import { paymentSchema } from "lib/db/schema.ts"
+
+/**
+ * POST /payments/cancel
+ *
+ * Cancel a pending payment. No-op if the payment is already in a terminal
+ * state — the existing record is returned unchanged. Returns
+ * `{ payment: null }` if the id doesn't exist.
+ */
+export default withRouteSpec({
+  methods: ["POST"],
+  jsonBody: z.object({
+    payment_id: z.string().min(1),
+  }),
+  jsonResponse: z.object({
+    payment: paymentSchema.nullable(),
+  }),
+})(async (req, ctx) => {
+  const { payment_id } = await req.json()
+  const updated = ctx.db.updatePaymentStatus(payment_id, "canceled")
+  return ctx.json({ payment: updated })
+})
diff --git a/routes/payments/complete.ts b/routes/payments/complete.ts
new file mode 100644
index 0000000..a5a9893
--- /dev/null
+++ b/routes/payments/complete.ts
@@ -0,0 +1,24 @@
+import { withRouteSpec } from "lib/middleware/with-winter-spec"
+import { z } from "zod"
+import { paymentSchema } from "lib/db/schema.ts"
+
+/**
+ * POST /payments/complete
+ *
+ * Mark a pending payment as `completed`. No-op if the payment is already in a
+ * terminal state — the existing record is returned unchanged. Returns
+ * `{ payment: null }` if the id doesn't exist.
+ */
+export default withRouteSpec({
+  methods: ["POST"],
+  jsonBody: z.object({
+    payment_id: z.string().min(1),
+  }),
+  jsonResponse: z.object({
+    payment: paymentSchema.nullable(),
+  }),
+})(async (req, ctx) => {
+  const { payment_id } = await req.json()
+  const updated = ctx.db.updatePaymentStatus(payment_id, "completed")
+  return ctx.json({ payment: updated })
+})
diff --git a/routes/payments/get.ts b/routes/payments/get.ts
new file mode 100644
index 0000000..20be721
--- /dev/null
+++ b/routes/payments/get.ts
@@ -0,0 +1,23 @@
+import { withRouteSpec } from "lib/middleware/with-winter-spec"
+import { z } from "zod"
+import { paymentSchema } from "lib/db/schema.ts"
+
+/**
+ * GET /payments/get
+ *
+ * Fetch a single payment by its `payment_id`. Returns `{ payment: null }` if
+ * not found rather than a 404 — keeps the response schema simple and lets
+ * clients branch on the body instead of HTTP status.
+ */
+export default withRouteSpec({
+  methods: ["GET"],
+  queryParams: z.object({
+    payment_id: z.string().min(1),
+  }),
+  jsonResponse: z.object({
+    payment: paymentSchema.nullable(),
+  }),
+})((req, ctx) => {
+  const payment = ctx.db.getPayment(req.query.payment_id)
+  return ctx.json({ payment })
+})
diff --git a/routes/payments/list.ts b/routes/payments/list.ts
new file mode 100644
index 0000000..315d999
--- /dev/null
+++ b/routes/payments/list.ts
@@ -0,0 +1,30 @@
+import { withRouteSpec } from "lib/middleware/with-winter-spec"
+import { z } from "zod"
+import { paymentSchema } from "lib/db/schema.ts"
+
+/**
+ * GET /payments/list
+ *
+ * Lists payments. Filter by `status`, `recipient`, or `repository`. With no
+ * filters set, returns all payments in creation order.
+ */
+export default withRouteSpec({
+  methods: ["GET"],
+  queryParams: z.object({
+    status: z
+      .enum(["pending", "completed", "canceled", "failed"])
+      .optional(),
+    recipient: z.string().optional(),
+    repository: z.string().optional(),
+  }),
+  jsonResponse: z.object({
+    payments: z.array(paymentSchema),
+  }),
+})((req, ctx) => {
+  const { status, recipient, repository } = req.query
+  let payments = ctx.db.payments
+  if (status) payments = payments.filter((p) => p.status === status)
+  if (recipient) payments = payments.filter((p) => p.recipient === recipient)
+  if (repository) payments = payments.filter((p) => p.repository === repository)
+  return ctx.json({ payments })
+})
diff --git a/routes/payments/send.ts b/routes/payments/send.ts
new file mode 100644
index 0000000..df0fb5a
--- /dev/null
+++ b/routes/payments/send.ts
@@ -0,0 +1,38 @@
+import { withRouteSpec } from "lib/middleware/with-winter-spec"
+import { z } from "zod"
+import { paymentSchema } from "lib/db/schema.ts"
+
+/**
+ * POST /payments/send
+ *
+ * Creates a pending payment. Provide an `idempotency_key` to make the call
+ * retry-safe — repeated sends with the same key return the same payment
+ * record rather than creating duplicates.
+ */
+export default withRouteSpec({
+  methods: ["POST"],
+  jsonBody: z.object({
+    recipient: z.string().min(1),
+    amount: z.number().positive(),
+    currency: z.string().default("USD"),
+    bounty_id: z.string().optional(),
+    issue_number: z.number().optional(),
+    repository: z.string().optional(),
+    idempotency_key: z.string().optional(),
+  }),
+  jsonResponse: z.object({
+    payment: paymentSchema,
+  }),
+})(async (req, ctx) => {
+  const body = await req.json()
+  const payment = ctx.db.addPayment({
+    recipient: body.recipient,
+    amount: body.amount,
+    currency: body.currency,
+    bounty_id: body.bounty_id ?? null,
+    issue_number: body.issue_number ?? null,
+    repository: body.repository ?? null,
+    idempotency_key: body.idempotency_key ?? null,
+  })
+  return ctx.json({ payment })
+})
diff --git a/tests/routes/payments/send.test.ts b/tests/routes/payments/send.test.ts
new file mode 100644
index 0000000..a582a21
--- /dev/null
+++ b/tests/routes/payments/send.test.ts
@@ -0,0 +1,113 @@
+import { getTestServer } from "tests/fixtures/get-test-server"
+import { test, expect } from "bun:test"
+
+test("POST /payments/send creates a pending payment", async () => {
+  const { axios } = await getTestServer()
+  const { data } = await axios.post("/payments/send", {
+    recipient: "alice",
+    amount: 100,
+    bounty_id: "algora-12345",
+    issue_number: 42,
+    repository: "example/repo",
+  })
+  expect(data.payment.recipient).toBe("alice")
+  expect(data.payment.amount).toBe(100)
+  expect(data.payment.currency).toBe("USD")
+  expect(data.payment.status).toBe("pending")
+  expect(data.payment.bounty_id).toBe("algora-12345")
+})
+
+test("POST /payments/send with idempotency_key dedupes retries", async () => {
+  const { axios } = await getTestServer()
+  const body = {
+    recipient: "bob",
+    amount: 50,
+    idempotency_key: "retry-once",
+  }
+  const a = await axios.post("/payments/send", body)
+  const b = await axios.post("/payments/send", body)
+  expect(a.data.payment.payment_id).toBe(b.data.payment.payment_id)
+
+  const list = await axios.get("/payments/list", { params: { recipient: "bob" } })
+  expect(list.data.payments).toHaveLength(1)
+})
+
+test("GET /payments/get returns the payment", async () => {
+  const { axios } = await getTestServer()
+  const { data: created } = await axios.post("/payments/send", {
+    recipient: "carol",
+    amount: 25,
+  })
+  const { data: fetched } = await axios.get("/payments/get", {
+    params: { payment_id: created.payment.payment_id },
+  })
+  expect(fetched.payment.payment_id).toBe(created.payment.payment_id)
+  expect(fetched.payment.recipient).toBe("carol")
+})
+
+test("GET /payments/get returns { payment: null } for unknown id", async () => {
+  const { axios } = await getTestServer()
+  const { data } = await axios.get("/payments/get", {
+    params: { payment_id: "does-not-exist" },
+  })
+  expect(data.payment).toBeNull()
+})
+
+test("POST /payments/complete moves pending → completed", async () => {
+  const { axios } = await getTestServer()
+  const { data: created } = await axios.post("/payments/send", {
+    recipient: "dave",
+    amount: 75,
+  })
+  const { data: completed } = await axios.post("/payments/complete", {
+    payment_id: created.payment.payment_id,
+  })
+  expect(completed.payment.status).toBe("completed")
+})
+
+test("POST /payments/cancel moves pending → canceled", async () => {
+  const { axios } = await getTestServer()
+  const { data: created } = await axios.post("/payments/send", {
+    recipient: "eve",
+    amount: 25,
+  })
+  const { data: canceled } = await axios.post("/payments/cancel", {
+    payment_id: created.payment.payment_id,
+  })
+  expect(canceled.payment.status).toBe("canceled")
+})
+
+test("completed payments stay completed (terminal state)", async () => {
+  const { axios } = await getTestServer()
+  const { data: created } = await axios.post("/payments/send", {
+    recipient: "frank",
+    amount: 10,
+  })
+  await axios.post("/payments/complete", {
+    payment_id: created.payment.payment_id,
+  })
+  // Try to cancel — should be a no-op since payment is terminal.
+  const { data: canceled } = await axios.post("/payments/cancel", {
+    payment_id: created.payment.payment_id,
+  })
+  expect(canceled.payment.status).toBe("completed")
+})
+
+test("GET /payments/list filters by status", async () => {
+  const { axios } = await getTestServer()
+  const { data: p1 } = await axios.post("/payments/send", {
+    recipient: "g",
+    amount: 1,
+  })
+  await axios.post("/payments/send", { recipient: "h", amount: 2 })
+  await axios.post("/payments/complete", { payment_id: p1.payment.payment_id })
+
+  const pending = await axios.get("/payments/list", {
+    params: { status: "pending" },
+  })
+  const completed = await axios.get("/payments/list", {
+    params: { status: "completed" },
+  })
+  expect(pending.data.payments).toHaveLength(1)
+  expect(completed.data.payments).toHaveLength(1)
+})