PA-DSS is a security standard for the payment application in the payment terminal. The PA DSS requirements make sure that the software is PCI DSS compliant. See list of PS DSS certified software.
PCI-PTS is a security standard for all terminals and other hardware used for handling PIN. All suppliers of PIN applications must comply with the requirements and the guidelines related to PTS.
Merchants must have a payment terminal with PA-DSS approved software in order to obtain a merchant agreement with Nets. Therefore, you must indicate in your application that you use an approved payment terminal.