Document is already exists with different section type
When you receive this error you need to check that document, it must be available in portal in any section.
You need to find the document in portal whether it could be in sales module, E invoice module, or other section type.
In order to replicate this issue firstly need to delete the Invoice in Sales module as well as in E-invoice module and after the document is deleted re-push the document as per your requirement and the E-invoice and Sales invoice will generated.