First you need to setup the number series(ScreenId=CS201010) for customerInvoice and either tick:
- Manual Numbering: This forces you to always set a reference number, even in the UI. You do this with the "referenceNumber" field.
Works on both v1 & v2
-Allow for manual numbering on import: This allows you to specify a reference number that does not follow the number series that is automatically applied. To use this, you need to set the field "overrideNumberSeries" to true and then set your "referenceNumber".
Please note that this function only works on the V2/customerInvoice.