Hello everyone,
I am working on Odoo 12 and trying to put a "Print Receipt" button on payments form for the model account.payment.
This is located under Invoicing | Customers | Payments and Invoicing | Vendors | Payments

Loooking into the code for the account.payment, I can see that there is an xml that puts an Action menu option for printing the Payment Receipt, so I want to use this report for my button.

The xml for the core "account.payment" is (report definition):

      <report
          id="action_report_payment_receipt"
          model="account.payment"
          string="Payment Receipt"
          report_type="qweb-pdf"
          name="account.report_payment_receipt"
          file="account.report_payment_receipt"
          menu="True"
      />

So, I have inherited the account.payment form view and was abble to put the print button there, by:

      <!-- PRINT RECEIPT BUTTON -->
     <record id="receipt_form_print_document" model="ir.ui.view">
        <field name="name">Print Receipt Button on Form</field>
        <field name="model">account.payment</field>
        <field name="inherit_id" ref="account.view_account_payment_form"/>
        <field name="arch" type="xml">
             <xpath expr="//header" position="inside">
                   <button name="document_print" string="Print Receipt" type="object" attrs="{'invisible':[('state', '==', 'draft')]}" icon="fa-print" class="oe_highlight" groups="base.group_user"/>
             </xpath>
        </field>
     </record>

The button is ok and is shown only when document is not in draft state.

For the button to work, I have inherited account.payment and entered the method "document_print" into it:

      class AccountPayment(models.Model):
     _inherit = 'account.payment'

     @api.multi
     def document_print(self):
          self.env.ref('account.action_report_payment_receipt').report_action(self)

The problem is that I can see the button, but when pressed nothing happens.
Odoo raises no error but the report is simple not printed.

I garantee that Odoo locates the "action" for the report, because if I change it, Odoo raises and error...

What I am missing here?

Thank you all in advance

Best regards

PM