diff --git a/apps/api/package.json b/apps/api/package.json
index c1dd783..fead9b8 100644
--- a/apps/api/package.json
+++ b/apps/api/package.json
@@ -7,7 +7,8 @@
     "dev": "nitro dev",
     "dev:inspect": "workflow inspect runs --web",
     "build": "nitro build",
-    "typecheck": "tsc --noEmit"
+    "typecheck": "tsc --noEmit",
+    "test": "bun test"
   },
   "dependencies": {
     "@ai-sdk/openai": "^3.0.52",
diff --git a/apps/api/src/__tests__/sendblue.test.ts b/apps/api/src/__tests__/sendblue.test.ts
new file mode 100644
index 0000000..cabd6b1
--- /dev/null
+++ b/apps/api/src/__tests__/sendblue.test.ts
@@ -0,0 +1,45 @@
+import { describe, expect, test } from "bun:test";
+
+process.env.SENDBLUE_API_KEY = "test-key";
+process.env.SENDBLUE_API_SECRET = "test-secret";
+process.env.SENDBLUE_FROM_NUMBER = "+15555550100";
+process.env.SENDBLUE_WEBHOOK_SECRET = "expected-secret";
+process.env.UPSTASH_REDIS_REST_URL = "https://example.upstash.io";
+process.env.UPSTASH_REDIS_REST_TOKEN = "test-token";
+process.env.REDIS_URL = "rediss://default:test@example.upstash.io:6379";
+process.env.OPENAI_API_KEY = "sk-test";
+process.env.ENCRYPTION_KEY = "0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef";
+
+const { parseInbound } = await import("../sendblue");
+
+const inboundBody = {
+  status: "RECEIVED",
+  is_outbound: false,
+  number: "+15555550123",
+  content: "hello",
+  media_url: "",
+  message_handle: "message-1",
+};
+
+describe("parseInbound", () => {
+  test("rejects webhook requests without a signing secret", () => {
+    expect(parseInbound(new Headers(), inboundBody)).toBeNull();
+  });
+
+  test("rejects webhook requests with an invalid signing secret", () => {
+    const headers = new Headers({ "sb-signing-secret": "wrong-secret" });
+
+    expect(parseInbound(headers, inboundBody)).toBeNull();
+  });
+
+  test("accepts Sendblue's documented signing secret header", () => {
+    const headers = new Headers({ "sb-signing-secret": "expected-secret" });
+
+    expect(parseInbound(headers, inboundBody)).toEqual({
+      phone: "+15555550123",
+      text: "hello",
+      imageUrl: undefined,
+      messageId: "message-1",
+    });
+  });
+});
diff --git a/apps/api/src/sendblue.ts b/apps/api/src/sendblue.ts
index 9d6272f..e0e28c3 100644
--- a/apps/api/src/sendblue.ts
+++ b/apps/api/src/sendblue.ts
@@ -11,11 +11,16 @@ export interface InboundMessage {
   messageId: string | undefined;
 }
 
-const SECRET_HEADERS = ["x-webhook-secret", "x-sendblue-signature", "sb-webhook-secret"];
+const SECRET_HEADERS = [
+  "sb-signing-secret",
+  "x-webhook-secret",
+  "x-sendblue-signature",
+  "sb-webhook-secret",
+];
 
 export function parseInbound(headers: Headers, body: unknown): InboundMessage | null {
   const secret = SECRET_HEADERS.reduce<string | null>((v, h) => v ?? headers.get(h), null);
-  if (secret && secret !== env.SENDBLUE_WEBHOOK_SECRET) return null;
+  if (!secret || secret !== env.SENDBLUE_WEBHOOK_SECRET) return null;
 
   const b = body as Record<string, unknown>;
   if (b.is_outbound || b.status !== "RECEIVED") return null;