I have defined a new invoice report through GUI which works fine:

<?xml version="1.0"?>
<t t-name="account.report_invoice_foobar_document">
<t t-call="header_foobar">
<div class="page">
...

I also define a new QWeb through GUI and name it header_foobar:

<header>
<pageTemplate>
<frame id="first" x1="1.3cm" y1="3.0cm" height="21.7cm" width="19.0cm"/>
...

However I can't call that header_foobar template from account.report_invoice_foobar_document.

I have also tried to configure an external ID, maybe I am missing something.

Any tip or suggestion is really welcomed. thanks