Install Merchantware Paylink on each workstation. You can have Merchant Warehouse support staff do this remotely. In the ABC Client go to Settings | Advanced Setup Options | Credit Card Processing. Choose the company first, and then choose Merchantware. In ABC, configure the CardProcessing record in the zero screen. Edit the ! record.
If using a Verifone 1000SE pinpad with a serial interface, the default settings are 1200 baud, even parity, 7 data bits, 1 stop bit. You will need to configure Paylink to these settings. Merchant Warehouse support apparently doesn’t know this.
Import the attached .742 if you don’t have a CardProcessing file structure.