diff --git a/packages/twitterapiio/index.ts b/packages/twitterapiio/index.ts
index 49225d56a..89b32f2ca 100644
--- a/packages/twitterapiio/index.ts
+++ b/packages/twitterapiio/index.ts
@@ -723,7 +723,12 @@ export function twitterapiio<const T extends TwitterApiIOPluginOptions>(
 
 			if (source === 'webhook') {
 				const res = await ctx.keys.get_webhook_signature();
-				return res ?? '';
+				if (!res) {
+					throw new Error(
+						'[auth-missing:twitterapiio:webhook_signature]: TwitterApiIO webhook signature is missing',
+					);
+				}
+				return res;
 			}
 
 			if (source === 'endpoint' && options.key) {
diff --git a/packages/twitterapiio/webhook.test.ts b/packages/twitterapiio/webhook.test.ts
new file mode 100644
index 000000000..60fb2d955
--- /dev/null
+++ b/packages/twitterapiio/webhook.test.ts
@@ -0,0 +1,94 @@
+import type { WebhookRequest } from 'corsair/core';
+import { verifyHmacSignature } from 'corsair/http';
+import { verifyTwitterApiIOWebhookSignature } from './webhooks/types';
+
+jest.mock('corsair/http', () => ({
+	verifyHmacSignature: jest.fn(),
+}));
+
+const mockedVerify = verifyHmacSignature as jest.Mock;
+
+describe('TwitterApiIO Webhooks', () => {
+	beforeEach(() => {
+		jest.clearAllMocks();
+	});
+
+	describe('Signature Verification', () => {
+		it('Should verify correct signature via HMAC SHA256', async () => {
+			mockedVerify.mockReturnValue(true);
+
+			const mockRequest: WebhookRequest<unknown> = {
+				payload: {},
+				rawBody: 'mock-body-string',
+				headers: {
+					'x-twitterapiio-signature': 'sha256=valid-signature',
+				},
+			};
+
+			const result = verifyTwitterApiIOWebhookSignature(
+				mockRequest,
+				'my-app-secret',
+			);
+
+			expect(mockedVerify).toHaveBeenCalledWith(
+				'mock-body-string',
+				'my-app-secret',
+				'sha256=valid-signature',
+				'sha256',
+			);
+			expect(result.valid).toBe(true);
+		});
+
+		it('should reject when verification fails', async () => {
+			mockedVerify.mockReturnValue(false);
+
+			const mockRequest: WebhookRequest<unknown> = {
+				payload: {},
+				rawBody: 'mock-body-string',
+				headers: {
+					'x-twitterapiio-signature': 'sha256=invalid-signature',
+				},
+			};
+
+			const result = verifyTwitterApiIOWebhookSignature(
+				mockRequest,
+				'my-app-secret',
+			);
+
+			expect(result.valid).toBe(false);
+		});
+
+		it('Should reject when webhook secret is missing', () => {
+			mockedVerify.mockReturnValue(false);
+
+			const mockRequest: WebhookRequest<unknown> = {
+				payload: {},
+				rawBody: 'mock-body-string',
+				headers: {},
+			};
+
+			const result = verifyTwitterApiIOWebhookSignature(mockRequest, '');
+
+			expect(result.valid).toBe(false);
+			expect(result.error).toMatch('Missing webhook secret');
+		});
+
+		it('Should reject when signature is missing with configured secret', () => {
+			mockedVerify.mockReturnValue(false);
+
+			const mockRequest: WebhookRequest<unknown> = {
+				payload: {},
+				rawBody: 'mock-body-string',
+				headers: {},
+			};
+
+			const result = verifyTwitterApiIOWebhookSignature(
+				mockRequest,
+				'my-app-secret',
+			);
+
+			expect(result.valid).toBe(false);
+			expect(result.error).toMatch('Missing x-twitterapiio-signature header');
+		});
+	});
+});
diff --git a/packages/twitterapiio/webhooks/types.ts b/packages/twitterapiio/webhooks/types.ts
index 64d8fb803..552eb0c03 100644
--- a/packages/twitterapiio/webhooks/types.ts
+++ b/packages/twitterapiio/webhooks/types.ts
@@ -85,8 +85,8 @@ export function verifyTwitterApiIOWebhookSignature(
 		| undefined;
 
 	if (!signature) {
-		// If no secret is configured, treat as valid
-		if (!secret) return { valid: true };
+		// If no secret is configured, treat as invalid
+		if (!secret) return { valid: false, error: 'Missing webhook secret' };
 		return { valid: false, error: 'Missing x-twitterapiio-signature header' };
 	}