diff --git a/src/schemas/sep24.ts b/src/schemas/sep24.ts
new file mode 100644
index 0000000..9cc5360
--- /dev/null
+++ b/src/schemas/sep24.ts
@@ -0,0 +1,22 @@
+import { z } from "zod";
+
+const memoType = z.enum(["text", "id", "hash"]);
+
+/** Shared SEP-24 parameter contract for deposit and withdrawal starts. */
+export const sep24InteractiveSchema = z
+  .object({
+    assetCode: z.string().trim().min(1).max(12),
+    anchorName: z.string().trim().min(1).max(120).optional(),
+    account: z.string().regex(/^G[A-Z2-7]{55}$/).optional(),
+    memo: z.string().trim().min(1).max(64).optional(),
+    memoType: memoType.optional(),
+    walletName: z.string().trim().min(1).max(120).optional(),
+  })
+  .superRefine((value, ctx) => {
+    if (value.memo && !value.memoType) {
+      ctx.addIssue({ code: "custom", path: ["memoType"], message: "memoType is required when memo is supplied" });
+    }
+    if (value.memoType && !value.memo) {
+      ctx.addIssue({ code: "custom", path: ["memo"], message: "memo is required when memoType is supplied" });
+    }
+  });
diff --git a/tests/routes/sep24.test.ts b/tests/routes/sep24.test.ts
index 8313ef4..b6ad5c9 100644
--- a/tests/routes/sep24.test.ts
+++ b/tests/routes/sep24.test.ts
@@ -1,5 +1,6 @@
 import { describe, it, expect, beforeEach, vi } from "vitest";
 import jwt from "jsonwebtoken";
+import { sep24InteractiveSchema } from "../../src/schemas/sep24";
 
 const h = vi.hoisted(() => {
   const prisma: any = {
@@ -344,3 +345,30 @@ describe("POST /api/sep24/callback — state updates", () => {
     expect(res.statusCode).toBe(200);
   });
 });
+
+describe("SEP-24 interactive parameters", () => {
+  it("accepts a valid asset and memo pair", () => {
+    const result = sep24InteractiveSchema.safeParse({
+      assetCode: "USDC",
+      account: "GAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA",
+      memo: "invoice-42",
+      memoType: "text",
+    });
+    expect(result.success).toBe(true);
+  });
+
+  it("rejects a memo without a memo type", () => {
+    const result = sep24InteractiveSchema.safeParse({ assetCode: "XLM", memo: "42" });
+    expect(result.success).toBe(false);
+  });
+
+  it("rejects an invalid account and unsupported memo type", () => {
+    const result = sep24InteractiveSchema.safeParse({
+      assetCode: "XLM",
+      account: "not-a-stellar-account",
+      memo: "42",
+      memoType: "binary",
+    });
+    expect(result.success).toBe(false);
+  });
+});