Follow these steps to start testing the USPS APIs:

1. Sign Up

Sign up for a CAT USPS Business Account using the Business Customer Gateway (BCG). 

2. Log In

Log in to the USPS Developer Portal using the CAT USPS Business Account you created in Step 1.

3. Create an App

After logging into the Developer Portal, click the Apps button from the Menu Bar and complete the following steps to create an App:

1.Click "Add App"
2.Enter your App Name (required)
3.Enter your Callback URL (optional)
4.Check the box to accept Terms and Conditions and Privacy Policy
5.Enter Description (optional)
6.Select API Product (required)
7.Click "Add App"

4. Retrieve your Consumer Key and Secret 

Select your App and retrieve your Consumer Key and Consumer Secret from the Credentials section. These credentials are required for the next step and for generating the OAuth Token.

5. Request App Authorization

The Payments API, Domestic Labels API, and International Labels API require your app to be linked to the default USPS test credentials. Before testing these APIs, you will need to send your Consumer Key (client_id) to APISupport@usps.gov with the subject of ‘Authorize CAT App’ to request this authorization.

Reminder: Consumer Key and Secret are not interchangeable between Test and Production environments.

6. Generate your OAuth Token

Review the OAuth 2.0 specifications for “Generate OAuth Tokens” and pass the Consumer Key and Consumer Secret obtained in Step 5 as the client_id and client_secret, respectively.

7. Try Out USPS APIs

Review the API Catalog for the detailed specifications on the available APIs. All USPS APIs require an OAuth Token to be conveyed in the Authorization header, using the Bearer Token scheme. Please reference the USPS Github page for a repository that contains example Postman requests and Curl commands.

Note: You must change endpoints from https://api.usps.com/ to https://api-cat.usps.com/ when accessing the testing environment.

Contact Us:

If you have questions, please contact us at APISupport@usps.gov. In your email, please include the following information:

•Your Name
•Company Name
•Contact Phone Number
•Developer Portal Username
•Developer Portal App Name
•URL being called (api.usps.com or api-cat.usps.com)
•Consumer Key/client_id
•Customer Registration ID (CRID)
•Mailer ID (MID)
•Country
•ZIP Code

**Do not include Consumer Secret (client_secret)