diff --git a/packages/nodes-base/credentials/WooCommerceApi.credentials.ts b/packages/nodes-base/credentials/WooCommerceApi.credentials.ts
index 6931ba78d2d..b69be3c46ae 100644
--- a/packages/nodes-base/credentials/WooCommerceApi.credentials.ts
+++ b/packages/nodes-base/credentials/WooCommerceApi.credentials.ts
@@ -54,14 +54,14 @@ export class WooCommerceApi implements ICredentialType {
 				requestOptions.qs = {};
 			}
 			Object.assign(requestOptions.qs, {
-				consumer_key: credentials.consumerKey,
-				consumer_secret: credentials.consumerSecret,
+				consumer_key: String(credentials.consumerKey || ''),
+				consumer_secret: String(credentials.consumerSecret || ''),
 			});
 		} else {
 			// Use HTTP Basic Auth
 			requestOptions.auth = {
-				user: credentials.consumerKey as string,
-				password: credentials.consumerSecret as string,
+				user: String(credentials.consumerKey || ''),
+				password: String(credentials.consumerSecret || ''),
 			};
 		}
 		return requestOptions;
diff --git a/packages/nodes-base/credentials/WooCommerceApi.test.ts b/packages/nodes-base/credentials/WooCommerceApi.test.ts
new file mode 100644
index 00000000000..e2f63db1b7b
--- /dev/null
+++ b/packages/nodes-base/credentials/WooCommerceApi.test.ts
@@ -0,0 +1,92 @@
+import { WooCommerceApi } from './WooCommerceApi.credentials';
+import type { ICredentialDataDecryptedObject, IHttpRequestOptions } from 'n8n-workflow';
+
+describe('WooCommerceApi', () => {
+	let wooCommerceApi: WooCommerceApi;
+
+	beforeEach(() => {
+		wooCommerceApi = new WooCommerceApi();
+	});
+
+	describe('authenticate', () => {
+		it('should use Basic Auth by default', async () => {
+			const credentials: ICredentialDataDecryptedObject = {
+				consumerKey: 'test_key',
+				consumerSecret: 'test_secret',
+				includeCredentialsInQuery: false,
+			};
+
+			const requestOptions: IHttpRequestOptions = {
+				url: 'https://example.com/api',
+			};
+
+			const result = await wooCommerceApi.authenticate(credentials, requestOptions);
+
+			expect(result.auth).toEqual({
+				user: 'test_key',
+				password: 'test_secret',
+			});
+			expect(result.qs).toBeUndefined();
+		});
+
+		it('should use query parameters when includeCredentialsInQuery is true', async () => {
+			const credentials: ICredentialDataDecryptedObject = {
+				consumerKey: 'test_key',
+				consumerSecret: 'test_secret',
+				includeCredentialsInQuery: true,
+			};
+
+			const requestOptions: IHttpRequestOptions = {
+				url: 'https://example.com/api',
+			};
+
+			const result = await wooCommerceApi.authenticate(credentials, requestOptions);
+
+			expect(result.qs).toEqual({
+				consumer_key: 'test_key',
+				consumer_secret: 'test_secret',
+			});
+			expect(result.auth).toBeUndefined();
+		});
+
+		it('should handle existing query parameters', async () => {
+			const credentials: ICredentialDataDecryptedObject = {
+				consumerKey: 'test_key',
+				consumerSecret: 'test_secret',
+				includeCredentialsInQuery: true,
+			};
+
+			const requestOptions: IHttpRequestOptions = {
+				url: 'https://example.com/api',
+				qs: { existing: 'param' },
+			};
+
+			const result = await wooCommerceApi.authenticate(credentials, requestOptions);
+
+			expect(result.qs).toEqual({
+				existing: 'param',
+				consumer_key: 'test_key',
+				consumer_secret: 'test_secret',
+			});
+		});
+
+		it('should handle non-string credentials gracefully', async () => {
+			const credentials: ICredentialDataDecryptedObject = {
+				consumerKey: null,
+				consumerSecret: undefined,
+				includeCredentialsInQuery: false,
+			};
+
+			const requestOptions: IHttpRequestOptions = {
+				url: 'https://example.com/api',
+			};
+
+			const result = await wooCommerceApi.authenticate(credentials, requestOptions);
+
+			expect(result.auth).toEqual({
+				user: '',
+				password: '',
+			});
+		});
+	});
+});