When you purchase a postage label on PayPal shipping, you select a price band, each price band has very precise restrictions in terms of Weight, Dimensions (Longest, Second Longest, Smallest side) and Overall size ( calculated by taking the two shortest sides of your parcel summed together. Then multiply the sum by 2 and finally add the length. The total is the overall size).
Such restrictions are visible from the service selection page before you purchase the postage label and they can change depending on the carrier, the service and the selected weight band. So it is important to carefully read them before you dispatch your parcel:
If when dispatching the parcel the weight or dimensions exceeds what is permitted by the price band you paid for you are infringing PayPal Shipping powered by Packlink sales conditions as stated by article 12 of Packlink terms and conditions.
Packlink does not physically handle parcels and after the parcel is dispatched, it is scanned at the chosen carrier's depot where it is weighted and measured by the carrier industrial sorter, producing a carrier audited measurement and weight.
The carrier then sends the audited measurements to Packlink and when Packlink detects a discrepancy between the weight or dimensions permitted for the price band you have paid for and the measurement and weight audited by the carrier, Packlink will issue to the sender an underpayment fee: Additional charges