This is a GP featured that I’ve fought for, begged for and even threatened people over. It’s finally here in GP 2015 R2. Microsoft Dynamics GP 2015 R2 Debits displayed before Credits in SmartList Reports
Microsoft Dynamics GP 2015 R2 Debits displayed before Credits in SmartList Reports – Microsoft Dynamics GP Community
Reporting & BIGP 2015
Archived post from 2015. Dynamics GP and the links it points to have changed since; check current documentation before relying on version-specific steps.