Welcome to the Community, DavidOM.
Let me share details of what will happen if you import your invoices with their own VAT calculations from different software to your QuickBooks Online (QBO) account.
When you import invoices with Value Added Tax (VAT) from another database to QBO, ensure the VAT codes are included in your invoices spreadsheet. This guarantees that the VAT codes will synchronize with the QBO VAT since QuickBooks will apply its own VAT calculation in its invoices. To know more about importing multiple invoices in QBO, visit this article t: Import invoices at once in QuickBooks Online.
In addition, check out this article to understand how VAT codes are utilized on the sales and purchase forms in QBO: VAT codes in QuickBooks Online: A complete guide.
Don't hesitate to return to this thread if you have further inquiries about importing invoices with VAT or QBO-related questions. I'll be sure to answer them as soon as possible. Have a great day ahead!