diff --git a/lib/db/db-client.ts b/lib/db/db-client.ts
index e525e65..2c55287 100644
--- a/lib/db/db-client.ts
+++ b/lib/db/db-client.ts
@@ -1,9 +1,15 @@
-import { createStore, type StoreApi } from "zustand/vanilla"
+import { hoist } from "zustand-hoist"
+import { combine } from "zustand/middleware"
 import { immer } from "zustand/middleware/immer"
-import { hoist, type HoistedStoreApi } from "zustand-hoist"
+import { createStore } from "zustand/vanilla"
 
-import { databaseSchema, type DatabaseSchema, type Thing } from "./schema.ts"
-import { combine } from "zustand/middleware"
+import {
+  type DatabaseSchema,
+  type Payment,
+  type PaymentStatus,
+  type Thing,
+  databaseSchema,
+} from "./schema.ts"
 
 export const createDatabase = () => {
   return hoist(createStore(initializer))
@@ -11,7 +17,7 @@ export const createDatabase = () => {
 
 export type DbClient = ReturnType<typeof createDatabase>
 
-const initializer = combine(databaseSchema.parse({}), (set) => ({
+const initializer = combine(databaseSchema.parse({}), (set, get) => ({
   addThing: (thing: Omit<Thing, "thing_id">) => {
     set((state) => ({
       things: [
@@ -21,4 +27,91 @@ const initializer = combine(databaseSchema.parse({}), (set) => ({
       idCounter: state.idCounter + 1,
     }))
   },
+  sendPayment: (
+    payment: Omit<
+      Payment,
+      | "payment_id"
+      | "status"
+      | "created_at"
+      | "updated_at"
+      | "completed_at"
+      | "cancelled_at"
+    >,
+  ) => {
+    const now = new Date().toISOString()
+    let createdPayment: Payment | undefined
+
+    set((state) => {
+      const existingPayment = payment.idempotency_key
+        ? state.payments.find(
+            (existing) => existing.idempotency_key === payment.idempotency_key,
+          )
+        : undefined
+
+      if (existingPayment) {
+        createdPayment = existingPayment
+        return {}
+      }
+
+      createdPayment = {
+        ...payment,
+        payment_id: state.paymentIdCounter.toString(),
+        status: "pending",
+        created_at: now,
+        updated_at: now,
+      }
+
+      return {
+        payments: [...state.payments, createdPayment],
+        paymentIdCounter: state.paymentIdCounter + 1,
+      }
+    })
+
+    return createdPayment!
+  },
+  listPayments: (filters?: {
+    status?: PaymentStatus
+    recipient?: string
+    repository?: string
+    bounty_id?: string
+  }) => {
+    const state = get()
+    return state.payments.filter((payment) => {
+      if (filters?.status && payment.status !== filters.status) return false
+      if (filters?.recipient && payment.recipient !== filters.recipient) {
+        return false
+      }
+      if (filters?.repository && payment.repository !== filters.repository) {
+        return false
+      }
+      if (filters?.bounty_id && payment.bounty_id !== filters.bounty_id) {
+        return false
+      }
+      return true
+    })
+  },
+  getPayment: (payment_id: string) => {
+    return get().payments.find((payment) => payment.payment_id === payment_id)
+  },
+  updatePaymentStatus: (payment_id: string, status: PaymentStatus) => {
+    const now = new Date().toISOString()
+    let updatedPayment: Payment | undefined
+
+    set((state) => ({
+      payments: state.payments.map((payment) => {
+        if (payment.payment_id !== payment_id) return payment
+
+        updatedPayment = {
+          ...payment,
+          status,
+          updated_at: now,
+          completed_at: status === "completed" ? now : payment.completed_at,
+          cancelled_at: status === "cancelled" ? now : payment.cancelled_at,
+        }
+        return updatedPayment
+      }),
+    }))
+
+    return updatedPayment
+  },
 }))
diff --git a/lib/db/schema.ts b/lib/db/schema.ts
index 8377516..0d9896d 100644
--- a/lib/db/schema.ts
+++ b/lib/db/schema.ts
@@ -9,8 +9,30 @@ export const thingSchema = z.object({
 })
 export type Thing = z.infer<typeof thingSchema>
 
+export const paymentStatusSchema = z.enum(["pending", "completed", "cancelled"])
+export type PaymentStatus = z.infer<typeof paymentStatusSchema>
+
+export const paymentSchema = z.object({
+  payment_id: z.string(),
+  recipient: z.string(),
+  amount: z.number(),
+  currency: z.string(),
+  status: paymentStatusSchema,
+  bounty_id: z.string().optional(),
+  issue_number: z.number().optional(),
+  repository: z.string().optional(),
+  idempotency_key: z.string().optional(),
+  created_at: z.string(),
+  updated_at: z.string(),
+  completed_at: z.string().optional(),
+  cancelled_at: z.string().optional(),
+})
+export type Payment = z.infer<typeof paymentSchema>
+
 export const databaseSchema = z.object({
   idCounter: z.number().default(0),
+  paymentIdCounter: z.number().default(0),
   things: z.array(thingSchema).default([]),
+  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..f0306c0
--- /dev/null
+++ b/routes/payments/cancel.ts
@@ -0,0 +1,27 @@
+import { paymentSchema } from "lib/db/schema"
+import { withRouteSpec } from "lib/middleware/with-winter-spec"
+import { z } from "zod"
+
+export default withRouteSpec({
+  methods: ["POST"],
+  jsonBody: z.object({
+    payment_id: z.string().min(1),
+  }),
+  jsonResponse: z.union([
+    z.object({
+      payment: paymentSchema,
+    }),
+    z.object({
+      error: z.string(),
+    }),
+  ]),
+})(async (req, ctx) => {
+  const { payment_id } = await req.json()
+  const payment = ctx.db.updatePaymentStatus(payment_id, "cancelled")
+
+  if (!payment) {
+    return ctx.json({ error: "payment not found" }, { status: 404 })
+  }
+
+  return ctx.json({ payment })
+})
diff --git a/routes/payments/complete.ts b/routes/payments/complete.ts
new file mode 100644
index 0000000..8c0fe1d
--- /dev/null
+++ b/routes/payments/complete.ts
@@ -0,0 +1,27 @@
+import { paymentSchema } from "lib/db/schema"
+import { withRouteSpec } from "lib/middleware/with-winter-spec"
+import { z } from "zod"
+
+export default withRouteSpec({
+  methods: ["POST"],
+  jsonBody: z.object({
+    payment_id: z.string().min(1),
+  }),
+  jsonResponse: z.union([
+    z.object({
+      payment: paymentSchema,
+    }),
+    z.object({
+      error: z.string(),
+    }),
+  ]),
+})(async (req, ctx) => {
+  const { payment_id } = await req.json()
+  const payment = ctx.db.updatePaymentStatus(payment_id, "completed")
+
+  if (!payment) {
+    return ctx.json({ error: "payment not found" }, { status: 404 })
+  }
+
+  return ctx.json({ payment })
+})
diff --git a/routes/payments/get.ts b/routes/payments/get.ts
new file mode 100644
index 0000000..5d3511b
--- /dev/null
+++ b/routes/payments/get.ts
@@ -0,0 +1,27 @@
+import { paymentSchema } from "lib/db/schema"
+import { withRouteSpec } from "lib/middleware/with-winter-spec"
+import { z } from "zod"
+
+export default withRouteSpec({
+  methods: ["GET"],
+  jsonResponse: z.union([
+    z.object({
+      payment: paymentSchema,
+    }),
+    z.object({
+      error: z.string(),
+    }),
+  ]),
+})((req, ctx) => {
+  const paymentId = new URL(req.url).searchParams.get("payment_id")
+  if (!paymentId) {
+    return ctx.json({ error: "payment_id is required" }, { status: 400 })
+  }
+
+  const payment = ctx.db.getPayment(paymentId)
+  if (!payment) {
+    return ctx.json({ error: "payment not found" }, { status: 404 })
+  }
+
+  return ctx.json({ payment })
+})
diff --git a/routes/payments/list.ts b/routes/payments/list.ts
new file mode 100644
index 0000000..616b6c8
--- /dev/null
+++ b/routes/payments/list.ts
@@ -0,0 +1,23 @@
+import { paymentSchema, paymentStatusSchema } from "lib/db/schema"
+import { withRouteSpec } from "lib/middleware/with-winter-spec"
+import { z } from "zod"
+
+export default withRouteSpec({
+  methods: ["GET"],
+  jsonResponse: z.object({
+    payments: z.array(paymentSchema),
+  }),
+})((req, ctx) => {
+  const searchParams = new URL(req.url).searchParams
+  const status = searchParams.get("status") ?? undefined
+  const parsedStatus = status ? paymentStatusSchema.parse(status) : undefined
+
+  const payments = ctx.db.listPayments({
+    status: parsedStatus,
+    recipient: searchParams.get("recipient") ?? undefined,
+    repository: searchParams.get("repository") ?? undefined,
+    bounty_id: searchParams.get("bounty_id") ?? undefined,
+  })
+
+  return ctx.json({ payments })
+})
diff --git a/routes/payments/send.ts b/routes/payments/send.ts
new file mode 100644
index 0000000..fa5b3cb
--- /dev/null
+++ b/routes/payments/send.ts
@@ -0,0 +1,37 @@
+import { paymentSchema } from "lib/db/schema"
+import { withRouteSpec } from "lib/middleware/with-winter-spec"
+import { z } from "zod"
+
+export default withRouteSpec({
+  methods: ["POST"],
+  jsonBody: z.object({
+    recipient: z.string().min(1),
+    amount: z.number().positive(),
+    currency: z.string().min(1).default("USD"),
+    bounty_id: z.string().min(1).optional(),
+    issue_number: z.number().int().positive().optional(),
+    repository: z.string().min(1).optional(),
+    idempotency_key: z.string().min(1).optional(),
+  }),
+  jsonResponse: z.object({
+    payment: paymentSchema,
+    reused: z.boolean(),
+  }),
+})(async (req, ctx) => {
+  const body = await req.json()
+  const existingPayment = body.idempotency_key
+    ? ctx.db.payments.find(
+        (payment) => payment.idempotency_key === body.idempotency_key,
+      )
+    : undefined
+
+  const payment = ctx.db.sendPayment({
+    ...body,
+    currency: body.currency ?? "USD",
+  })
+
+  return ctx.json({
+    payment,
+    reused: Boolean(existingPayment),
+  })
+})
diff --git a/tests/routes/payments/lifecycle.test.ts b/tests/routes/payments/lifecycle.test.ts
new file mode 100644
index 0000000..45196fc
--- /dev/null
+++ b/tests/routes/payments/lifecycle.test.ts
@@ -0,0 +1,91 @@
+import { expect, test } from "bun:test"
+import { getTestServer } from "tests/fixtures/get-test-server"
+
+test("sends, retrieves, lists, and completes a payment", async () => {
+  const { axios } = await getTestServer()
+
+  const { data: sendData } = await axios.post("/payments/send", {
+    recipient: "octocat",
+    amount: 10,
+    currency: "USD",
+    bounty_id: "bounty-1",
+    issue_number: 1,
+    repository: "tscircuit/fake-algora",
+  })
+
+  expect(sendData.reused).toBe(false)
+  expect(sendData.payment).toMatchObject({
+    payment_id: "0",
+    recipient: "octocat",
+    amount: 10,
+    currency: "USD",
+    bounty_id: "bounty-1",
+    issue_number: 1,
+    repository: "tscircuit/fake-algora",
+    status: "pending",
+  })
+
+  const { data: getData } = await axios.get(
+    `/payments/get?payment_id=${sendData.payment.payment_id}`,
+  )
+  expect(getData.payment.payment_id).toBe(sendData.payment.payment_id)
+
+  const { data: listData } = await axios.get(
+    "/payments/list?status=pending&repository=tscircuit/fake-algora",
+  )
+  expect(listData.payments).toHaveLength(1)
+
+  const { data: completeData } = await axios.post("/payments/complete", {
+    payment_id: sendData.payment.payment_id,
+  })
+  expect(completeData.payment.status).toBe("completed")
+  expect(typeof completeData.payment.completed_at).toBe("string")
+})
+
+test("reuses a payment when the idempotency key matches", async () => {
+  const { axios } = await getTestServer()
+
+  const payload = {
+    recipient: "octocat",
+    amount: 25,
+    currency: "USD",
+    idempotency_key: "github-delivery-1",
+  }
+
+  const { data: firstSend } = await axios.post("/payments/send", payload)
+  const { data: retrySend } = await axios.post("/payments/send", payload)
+  const { data: listData } = await axios.get("/payments/list")
+
+  expect(firstSend.reused).toBe(false)
+  expect(retrySend.reused).toBe(true)
+  expect(retrySend.payment.payment_id).toBe(firstSend.payment.payment_id)
+  expect(listData.payments).toHaveLength(1)
+})
+
+test("filters payments and cancels pending payments", async () => {
+  const { axios } = await getTestServer()
+
+  await axios.post("/payments/send", {
+    recipient: "alice",
+    amount: 5,
+    repository: "owner/repo-a",
+  })
+  const { data: secondSend } = await axios.post("/payments/send", {
+    recipient: "bob",
+    amount: 15,
+    repository: "owner/repo-b",
+  })
+
+  const { data: filteredData } = await axios.get(
+    "/payments/list?recipient=alice",
+  )
+  expect(filteredData.payments).toHaveLength(1)
+  expect(filteredData.payments[0].recipient).toBe("alice")
+
+  const { data: cancelData } = await axios.post("/payments/cancel", {
+    payment_id: secondSend.payment.payment_id,
+  })
+
+  expect(cancelData.payment.status).toBe("cancelled")
+  expect(typeof cancelData.payment.cancelled_at).toBe("string")
+})