Some of our inventory G/L codes are changing to wrong code after invoicing, most our data is processed in Tradify & export to QB, can you assist to stop this happening ?

Welcome and thanks for visiting the Community, @service25. I understand how important the codes of your inventory. 

Since your data is processed in Tradify, you can import them to QuickBooks Online (QBO) through a third-party app. check this link to view the apps that can be linked to QuickBooks Online: https://apps.intuit.com/app/apps/home?collectionId.

This will help you import all your inventory and won't affect your codes when creating an invoice. 

For future reference, read through this help article: Set up and track your inventory in QuickBooks Online. It helps you learn about how to use the inventory in Quickbooks. 

Let me know if you have additional questions. We're always around to help.