diff --git a/apps/api/src/routes/invoices.ts b/apps/api/src/routes/invoices.ts
index 0f65a34..2714be4 100644
--- a/apps/api/src/routes/invoices.ts
+++ b/apps/api/src/routes/invoices.ts
@@ -8,6 +8,7 @@ import {
   invoices,
   invoiceLineItems,
   invoiceTipSplits,
+  refunds,
   appointments,
   services,
   clients,
@@ -125,8 +126,8 @@ const tipSplitSchema = z.object({
     })
   ).min(1).refine(
     (splits) => {
-      const total = splits.reduce((sum, s) => sum + s.sharePct, 0);
-      return Math.abs(total - 100) < 0.01;
+      const totalBps = splits.reduce((sum, s) => sum + Math.round(s.sharePct * 100), 0);
+      return totalBps === 10000;
     },
     { message: "Split percentages must sum to 100" }
   ),
@@ -170,12 +171,13 @@ invoicesRouter.post(
       }
     });
 
-    const splits = await db
-      .select()
-      .from(invoiceTipSplits)
-      .where(eq(invoiceTipSplits.invoiceId, id));
+    const [updatedInvoice] = await db.select().from(invoices).where(eq(invoices.id, id));
+    const [lineItems, tipSplits] = await Promise.all([
+      db.select().from(invoiceLineItems).where(eq(invoiceLineItems.invoiceId, id)),
+      db.select().from(invoiceTipSplits).where(eq(invoiceTipSplits.invoiceId, id)),
+    ]);
 
-    return c.json(splits, 201);
+    return c.json({ ...updatedInvoice, lineItems, tipSplits }, 201);
   }
 );
 
@@ -300,6 +302,13 @@ invoicesRouter.post("/from-appointment/:appointmentId", async (c) => {
   return c.json({ ...invoice, lineItems: [lineItem] }, 201);
 });
 
+const ALLOWED_TRANSITIONS: Record<string, string[]> = {
+  draft: ["pending", "void"],
+  pending: ["draft", "paid", "void"],
+  paid: ["void"],
+  void: [],
+};
+
 // Update invoice
 invoicesRouter.patch(
   "/:id",
@@ -315,8 +324,14 @@ invoicesRouter.patch(
       .where(eq(invoices.id, id));
     if (!current) return c.json({ error: "Not found" }, 404);
 
-    if (current.status === "void") {
-      return c.json({ error: "Cannot modify a voided invoice" }, 422);
+    if (body.status !== undefined) {
+      const allowed = ALLOWED_TRANSITIONS[current.status] ?? [];
+      if (!allowed.includes(body.status)) {
+        return c.json(
+          { error: `Invalid status transition from ${current.status} to ${body.status}` },
+          422
+        );
+      }
     }
 
     const update: Record<string, unknown> = { ...body, updatedAt: new Date() };
@@ -354,6 +369,7 @@ import { processRefund } from "../services/payment.js";
 
 const refundSchema = z.object({
   amountCents: z.number().int().nonnegative().optional(),
+  idempotencyKey: z.string().max(255).optional(),
 });
 
 invoicesRouter.post(
@@ -379,9 +395,28 @@ invoicesRouter.post(
       return c.json({ error: "No Stripe payment intent found for this invoice" }, 422);
     }
 
-    const result = await processRefund(id, body.amountCents);
-    if (!result) return c.json({ error: "Refund failed" }, 500);
+    return await db.transaction(async (tx) => {
+      if (body.idempotencyKey) {
+        const [existing] = await tx
+          .select()
+          .from(refunds)
+          .where(eq(refunds.idempotencyKey, body.idempotencyKey));
+        if (existing) {
+          return c.json({ refundId: existing.stripeRefundId });
+        }
+      }
 
-    return c.json({ refundId: result.refundId });
+      const result = await processRefund(id, body.amountCents);
+      if (!result) return c.json({ error: "Refund failed" }, 500);
+
+      await tx.insert(refunds).values({
+        invoiceId: id,
+        stripeRefundId: result.refundId,
+        idempotencyKey: body.idempotencyKey ?? null,
+        amountCents: body.amountCents ?? null,
+      });
+
+      return c.json({ refundId: result.refundId });
+    });
   }
 );
diff --git a/packages/db/migrations/0027_refunds.sql b/packages/db/migrations/0027_refunds.sql
new file mode 100644
index 0000000..ba8d6ea
--- /dev/null
+++ b/packages/db/migrations/0027_refunds.sql
@@ -0,0 +1,11 @@
+CREATE TABLE "refunds" (
+  "id" uuid PRIMARY KEY DEFAULT gen_random_uuid(),
+  "invoice_id" uuid NOT NULL REFERENCES "invoices"("id") ON DELETE RESTRICT,
+  "stripe_refund_id" text NOT NULL,
+  "idempotency_key" text UNIQUE,
+  "amount_cents" integer,
+  "created_at" timestamp NOT NULL DEFAULT NOW()
+);
+
+CREATE INDEX "idx_refunds_invoice_id" ON "refunds"("invoice_id");
+CREATE INDEX "idx_refunds_idempotency_key" ON "refunds"("idempotency_key");
diff --git a/packages/db/migrations/meta/_journal.json b/packages/db/migrations/meta/_journal.json
index 96da64a..c5ad96e 100644
--- a/packages/db/migrations/meta/_journal.json
+++ b/packages/db/migrations/meta/_journal.json
@@ -190,6 +190,13 @@
       "when": 1775568867192,
       "tag": "0026_stripe_payment",
       "breakpoints": true
+    },
+    {
+      "idx": 27,
+      "version": "7",
+      "when": 1775655267192,
+      "tag": "0027_refunds",
+      "breakpoints": true
     }
   ]
 }
\ No newline at end of file
diff --git a/packages/db/src/schema.ts b/packages/db/src/schema.ts
index a5d6bfc..375bf75 100644
--- a/packages/db/src/schema.ts
+++ b/packages/db/src/schema.ts
@@ -300,6 +300,25 @@ export const invoiceTipSplits = pgTable(
   (t) => [index("idx_invoice_tip_splits_invoice_id").on(t.invoiceId)]
 );
 
+// Refund records with idempotency key support
+export const refunds = pgTable(
+  "refunds",
+  {
+    id: uuid("id").primaryKey().defaultRandom(),
+    invoiceId: uuid("invoice_id")
+      .notNull()
+      .references(() => invoices.id, { onDelete: "restrict" }),
+    stripeRefundId: text("stripe_refund_id").notNull(),
+    idempotencyKey: text("idempotency_key").unique(),
+    amountCents: integer("amount_cents"),
+    createdAt: timestamp("created_at").notNull().defaultNow(),
+  },
+  (t) => [
+    index("idx_refunds_invoice_id").on(t.invoiceId),
+    index("idx_refunds_idempotency_key").on(t.idempotencyKey),
+  ]
+);
+
 // Tracks which reminder emails have been sent per appointment (prevents duplicates).
 // reminder_type values: "confirmation", "24h", "2h"
 export const reminderLogs = pgTable(