If you are planning to allow your customers to use the COD payment method for orders shipped with USPS shipping methods, you can make the calculation of shipping costs faster by setting a fixed extra fee for using the COD payment method.<br /><br />If a fixed amount COD fee is not set on the store's end, it will be calculated on the USPS end, and to get information about the COD fee amount the store will need to send several requests to the USPS API (one for each USPS service type), which may take up to 14 seconds. When using a fixed amount COD fee, the store will only send a single request to the USPS API, which will take under one second.<br /><br />Using a <b>fixed amount COD fee</b> allows the store to calculate the shipping cost much faster and is the <b>recommended option</b>.