USPS Shipping Add-On Setup Instructions

To enable real-time USPS shipping rates for your customers, you’ll need a USPS Web Tools API account. Follow the steps below to create an account and activate the required API access.

Step 1: Create a USPS Web Tools API Account

Visit the USPS Web Tools Portal to sign up for a legacy Web Tools API account.
After registration, you’ll receive an email titled “Important USPS Web Tools Registration Notice” containing your USER ID and Password.
These credentials are for the Web Tools APIs used by the USPS Shipping Method plugin.
Copy your USER ID and paste it into your site at Cartloom > Add-ons > USPS.
Note: Only the USER ID is required in the plugin settings. The password is not needed.

USPS must manually activate API access before your shipping rates can function. Continue to the next step to request access.

Step 2: Request USPS API Access

After creating your account, send an email to request access to the following APIs:

RateV4
IntlRateV2

If access isn’t granted, you'll receive an error like: API Authorization failure. User [Your User ID] is not authorized to use API RateV4.

To request access, send an email with the following details:

Email To: webtools@usps.gov
Subject: Web Tools API Access Request

Include this information in the body of the email:

Web Tools USER ID: (from your registration email)
USPS Mailer ID: “I am a Cartloom merchant and do not have my own Mailer ID.”
Company Website: e.g., www.yourstore.com
List of APIs: “The Rate Calculator APIs (RateV4 and IntlRateV2)”
Expected volume: e.g., “Not known”
Are you a shipper or software provider? “Shipper. Our business will be using the Web Tools Rate Calculator APIs to display USPS rates at checkout to customers in our ecommerce shop.”
Third-party software: “Cartloom”

Email Template:

Web Tools USER ID: [Your USER ID]

USPS Mailer ID: I am a Cartloom merchant and do not have my own Mailer ID.

Company Website: [Your website URL]

List the API(s) for which you are requesting access: The Rate Calculator APIs (RateV4 and IntlRateV2).

Expected volume: [Enter if known, or use "Not known"]

Are you a shipper or software provider? Please provide details on how your business will use the APIs:
Shipper. Our business will be using the Web Tools Rate Calculator APIs to display USPS rates at checkout to customers in our ecommerce shop.

Third-party software/software provider: Cartloom

Step 3: Configure the Plugin

Once access is granted, go to Cartloom > Add-Ons > USPS.
Enter your Web Tools USER ID in the appropriate field.
Adjust settings as needed to match your shipping preferences.

You're all set! Live USPS rates will now appear at checkout for your customers.

Need Help?

If you don’t receive the registration email within 24 hours, reach out via the USPS API support form.

For access-related questions, contact: webtools@usps.gov

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USPS Shipping Add-On Setup Instructions