You should always an integration before switching to Live.
To test your integration watch this video: Paragon ACH and Card Test
Check the Live checkbox on the Paragon Payment Processor record.
Default payment processor on individual Customer master?
Go to Customer>Profile> tab Payment Processor and select Paragon (or whatever you called it).
Configure TAP payments via Paragon
If you are using the TAP (Trade Acceleration Portal) you'll need to enable Card and ACH payments.
Go to Configuration for - TAPNAME>Basic configuration options for Customers>Configure>Taking Payments and check the appropriate boxes.
You need to be logged in as Salesorder system administrator to access the TAP configuration. The TAP configuration is accessible via the Gear icon on the TAP login page or in the footer bar when logged in.