We use electronic invoices from Odoo CE 15 in the ubl_bis3 format. When sending the invoices to the peppol Id, these xml files are rejected since they lack the XML declaration in the first line. When we edit the files and add these declaration manually, everything works fine and the xml-files are accepted by the system.

After all I wonder why the xml-declaration is missing, since in the code of account_edi_format.py is added already in line 209.

We tried to add the following lines to the template in /addons/account_edi_ubl_bis3/data/bis3_templates.xml, but this have no effect.

Where could we add this declaration in the code so that the generated xml-files are valid?