@Jonny @toplakd
Thanks, your ideas are great. Unfortunately I did not think about that and try to deactivate the codes for the last page of the order. To use the last page only as an order summary. I think that the deletion button should be deactivated as well.
As an example shipping from 100 euros free shipping and it will be deleted something, the shipping is not updated and as a seller you have to pay extra for his calculation.
Unfortunately, it is a bit user-friendly for the customer.
Presumably, the problem with me is that the one-page checkout (OPC) problems are not functioning correctly and I can not use it (AEUC, etc.).
I have not tested the module of @datakick yet, but on its demo page, it also does not seem to work properly. At least in the demo the settings are limited and can not test it completely. Here I miss a few things in the order overview, for example, AGB (terms & conditions), or the display price with VAT or the required line of VAT included.
TB works much better and faster than PS.
Only for the order process I have not found a suitable solution for me.