mail_template_data.xml

<?xml version="1.0" encoding="utf-8" ?>
<odoo noupdate="1">
    <record id="email_template_signup" model="mail.template">
        <field name="name">Event: Transferring started</field>
        <!--<field name="email_from">${(object.partner_id.email or '')|safe}</field>-->
        <field name="subject">Finish ticket transferring</field>
        <field name="partner_to">{{ object.attendee_partner_id.id }}</field>
        <field name="model_id" ref="event.model_event_registration" />
        <field name="auto_delete" eval="True" />
        <field name="lang">{{ object.attendee_partner_id.lang }}</field>
        <field
            name="body_html"
        ><![CDATA[

        <p>
            Hello <t t-out="object.attendee_partner_id.name" />,<br />

            The ticket transferring was initiated. Open the link below to complete to process:

                    <div style="padding:0px;width:600px;margin:auto;background: #FFFFFF repeat top /100%;color:#777777">
                        <div style="text-align: center; margin-top: 16px;">
                             <a t-attf-href="/my/registrations/transfer/receive?transfer_ticket={{ object.id }}" style="padding: 5px 10px; font-size: 12px; line-height: 18px; color: #FFFFFF; border-color:#875A7B; text-decoration: none; display: inline-block; margin-bottom: 0px; font-weight: 400; text-align: center; vertical-align: middle; cursor: pointer; white-space: nowrap; background-image: none; background-color: #875A7B; border: 1px solid #875A7B; border-radius:3px">Finish ticket transferring</a>
                        </div>
                    </div>
        </p>
        <p>
        </p>
        <p>Best regards,</p>

        ]]></field>
    </record>
</odoo>