For setting up NMI, you will need following data
Private API Key
Public API Key
In-order to obtain the values of Private and Public API Keys, login to the NMI gateway dashboard and head over to the “Security Keys” section under “My Settings” dropdown as shown in the screenshots below
Click on “Add a New Private Key” to create a new Private key
Now you should provide a Key Name and assign it to the Username and enable “API” checkbox.
Similarly, you can create a Public API Key by following the steps mentioned above,