USPS handles under-paid and over-paid postage labels with their Automated Package Verification (APV) system. The USPS APV program will verify correct postage has been paid on every domestic package, based on weight, dimensions, package type, mailing service, and the origin and destination ZIP codes.
As domestic shipments go through processing, USPS will scan and weigh them to check for correct postage paid based on size, weight, destination, mailing service, etc. Discounted rates such as Commercial Pricing and Cubic discounts are considered in the calculation.
If the amount is underpaid, a debit will be made to cover the difference. If the amount is overpaid, credit should be issued. These debits and credits will be shown as "Adjustments" in your USPS postage account. This change affects USPS Click-N-Ship and all PC Postage providers (e.g., ShippingEasy, Stamps.com).
Here are some of the most common reasons improper postage amounts are paid:
Package weight and/or dimensions entered during label printing do not match the actual shipment.
Incorrect packaging is used. Ex: Flat Rate label is used with a non-Flat Rate box shipment.
Improper service is used. Ex: First Class label on 1lb+ package.
Here are some tips to avoid incorrect postage:
Calibrate your scales daily.
Review your packaging with warehouse staff. Does your staff know the difference between a Small Flat Rate Box vs. a Medium Flat Rate Box? What about the different Flat Rate Envelopes?
Verify that the return address matches your warehouse location.
All of these transactions will be handled and visible through your USPS postage account, not in the ShippingEasy app.
To view adjustment details:
Login to Stamps.com using the Username and Password as shown in ShippingEasy.
Click the History tab to view the adjustment amounts in the Adj. Amount column.
This will show the amount adjusted for each transaction.
The adjustments will be debited or credited from the USPS postage account used to purchase the label.
If you are charged for underpaid postage but do not have money in your USPS postage account, the payment source attached to your USPS postage account will be charged to cover the adjustment amount.
The minimum postage purchase is $10, so if the adjustment requires more funds than are available in your USPS postage account, at least $10 will be purchased to cover the cost. Any unused funds will remain in your USPS postage account for future label purchases.
For ShippingEasy merchants, once the APV charges are disputed and approved, the system will automatically credit the adjusted amounts back to your Stamps.com account.
If you feel you were debited in error, you can dispute the charge with the USPS. You will need to contact the USPS Automated Package Verification department directly. Email VerifyPostageHelp@usps.gov or call 1-844-819-5187, and provide as much of the below information as possible:
Adjustment ID from your USPS postage account.
The last four digits of the Tracking Number.
The reason or explanation for the dispute (with as much detail as possible).