In order to display list of invoices, I follow this path: Project->Billing-> Invoices.

However, in the table listing them, I cannot find the project name so I tried to customize it as below (line in bold):

<?xml version="1.0"?>
<tree colors="blue:state == 'draft';black:state in ('proforma','proforma2','open');gray:state == 'cancel'" string="Invoice">
    <field name="partner_id" groups="base.group_user"/>
    <field name="date_invoice"/>
    <field name="number"/>
    <field name="reference" invisible="1"/>
    <field name="project_id"/>
    <field name="journal_id" invisible="1"/>
    <field name="period_id" invisible="1" groups="account.group_account_user"/>
    <field name="company_id" groups="base.group_multi_company" widget="selection"/>
    <field name="user_id"/>
    <field name="date_due"/>
    <field name="origin"/>
    <field name="currency_id" groups="base.group_multi_currency"/>
    <field name="residual" sum="Residual Amount"/>
    <field name="amount_untaxed" sum="Untaxed Amount"/>
    <field name="amount_total" sum="Total Amount"/>
    <field name="state"/>
</tree>

Unfortunately it didn't work and this is what I've got: "ValidateError, Error occurred while validating the field(s) arch: Invalid XML for View Architecture!"

Thanks for help