Hi found it.

I was looking for the solution on the python files but in fact it is on the xml.

Under "website_sale" we have the template "payment_confirmation_status".

I simple inherited:

    <div t-if="payment_tx_id.acquirer_id.post_msg" t-att-class="'card-body %s' % (
                    (payment_tx_id.state == 'pending' and 'bg-info-light') or
                    (payment_tx_id.state == 'done' and 'bg-success-light') or
                    (payment_tx_id.state == 'authorized' and 'bg-success-light') or
                    'bg-danger-light')">
                    <t t-raw="payment_tx_id.acquirer_id.post_msg" />
                    <div t-if="payment_tx_id.acquirer_id.provider == 'transfer' and order.reference">
                        <b>Communication: </b><span t-esc='order.reference'/>
                  </div>
     </div>

...and added my own code here.

Thank you

Best regards