You can use the Batch Transactions feature when importing your invoices with custom fields, wrivers.

QuickBooks Online has specific requirements for importing data, as it only allows certain fields for each data type. In your case, it's essential to create a custom field in QuickBooks Online (QBO) that aligns with the invoice details. This custom field will ensure that the data maps correctly during the import process.

Then, open your CSV file in Excel and manually align the invoice details with the custom field, specifically using the Batch Transactions columns. This step is crucial to ensure that the transactions import successfully. For further guidance on creating custom fields, see this article: Create and edit custom fields.

I've also added a screenshots for visual reference.

For more details about data imports in QuickBooks Online, see this article: Common questions about importing data to QuickBooks Online.

However, if you intend to include custom fields for the invoice number, you must enable the Custom transaction number feature in the Gear icon. This will allow it to appear directly in the Batch transactions column without the need for a custom field.

You can also use a third-party app to easily import invoices with custom fields. For a better view, visit this link: QBO App's store. There, you'll find various apps that work well with QuickBooks Online.

If you have additional questions about QuickBooks, leave a comment below. We're here to help.