Importing Quotes or Invoices with line items (products)


Can someone help me with the following issue please. I have created our products/services in the Products module. I have a cvs with quotes. In the csv are are also the quoted line times. How can I import the quotes with the line items?

Importing quotes without line items is working. It seems that in the import Quotes module there is no relation for products.

Thank you in advance.

Best regards,