Each time you validate and/or barcode an address one POSTman Web Service credit is used, even if that address could not be validated. Each time the "near matches" facility is used, two additional credits are used.
If you use the POSTman Web Service service directly either in your website, or if you use any other application that utilises POSTman Web Service one credit will be used each time an address is validated and/or barcoded. If a near matches facility is available, two additional credits will be used each time it is used.