I am new to odoo, while generating an invoice an error occurred like Failed to render template %r using values %r.  And I have added the full trace of the error below.

Traceback (most recent call last):
File "/opt/odoo13/addons/payment/controllers/portal.py", line 104, in payment_status_poll
tx_to_process._post_process_after_done()
File "/opt/odoo13/addons/payment/models/payment_acquirer.py", line 872, in _post_process_after_done
self._reconcile_after_transaction_done()
File "/opt/odoo13/addons/sale/models/payment.py", line 112, in _reconcile_after_transaction_done
sales_orders._send_order_confirmation_mail()
File "/opt/odoo13/addons/sale/models/sale.py", line 817, in _send_order_confirmation_mail
order.with_context(force_send=True).message_post_with_template(template_id, composition_mode='comment', email_layout_xmlid="mail.mail_notification_paynow")
File "/opt/odoo13/addons/mass_mailing/models/mail_thread.py", line 37, in message_post_with_template
return super(MailThread, no_massmail).message_post_with_template(template_id, **kwargs)
File "/opt/odoo13/addons/mail/models/mail_thread.py", line 1998, in message_post_with_template
update_values = composer.onchange_template_id(template_id, kwargs['composition_mode'], self._name, res_id)['value']
File "/opt/odoo13/addons/mail/wizard/mail_compose_message.py", line 405, in onchange_template_id
values = self.generate_email_for_composer(template_id, [res_id])[res_id]
File "/opt/odoo13/addons/mail/wizard/mail_compose_message.py", line 538, in generate_email_for_composer
template_values = self.env['mail.template'].with_context(tpl_partners_only=True).browse(template_id).generate_email(res_ids, fields=fields)
File "/opt/odoo13/addons/mail/models/mail_template.py", line 401, in generate_email
generated_field_values = Template._render_template(
File "/opt/odoo13/addons/mail/models/mail_template.py", line 290, in _render_template
raise UserError(_("Failed to render template %r using values %r") % (template, variables)