Line Items in a Custom Module

Dear SuiteCRM community,

I created the custom module Lieferscheine (delivery notes). The basis is the contract. Workflow: quote -> contract -> delivery notes (Lieferscheine). To create the delivery notes (Lieferscheine) I use createContract.php, in the contract module.
All data are transferred correctly, except the “line items”. These are neither displayed in detailview nor in editview. Only this is shown in editview:

But when a delivery note is printed in a PDF, all datas are displayed, includ the “line items”.

What did I make wrong? What I have to do, so that I can edit the positions in the editview?

Does it have to do with realationship ?:

Can someone help me, please. I would be very happy about it