Hi,

In the account module, the "_render_qweb_pdf" function triggers a check to verify if the invoice type is designated as an "entry". If any of the invoices fall into this category, it prompts a pop-up notification displaying a UserError message stating, "Only invoices can be printed."

 if any(x.move_type == 'entry' for x in invoices):

    raise UserError(_("Only invoices could be printed."))

Hope it helps