Thank you so much, I really appreciate it! No need to store the ID. After completeing the form it will be sent back to the SharePoint forms library where the data will be processed as is.
Short explanation....
ID-nummer is the field where to put the order number. That field has a rule and retreives infromation from the Order SharePoint list and populates all the fields except Adress, Telefon, Kontaktperson and Noteringar.
The Field Företag has a rule that collects information from another SharePoint list, Contacts. It fills out the fields Adress, Kontaktperson and Telefon.
The fields Företag and Registreringsnummer gets the ID column from the SharePoint list, it's the right corresponding ID to the post but it shows the ID instead of the company name and registration number.