header in custom invoice

I have checked show header on each page however i don’t see my header
which is the pdfmake syntax for the header when designing invoice ?

You can use the ‘Header’ tab on /settings/customize_design to set it.

Is there any chance you’re talking about the custom logo on the invoice header? If so, I had to use a makeshift solution to put the logo on my invoice headers because pdfmake does seem to have trouble loading image files on some browsers.