Legacy ERP migrations rarely fail because of technology. They fail because nobody knows what the old system quietly does at 3 a.m. This is a test article: the text is placeholder content to check the layout.
Start with a dependency map
List every report, export, scheduled job and integration. Treat anything undocumented as critical until proven otherwise, and ask the people who use it every day.
Run both systems side by side
Send the same transactions through both systems for a few weeks and compare outputs. Differences point to forgotten business rules.
Cut over in small batches
Move one business unit at a time, keep the rollback plan short, and agree in advance who can call it off.
