Hi,

The issue is that the dynamic values like {{ object.partner_id.display_name }} are written in Jinja syntax, which isn’t supported in Odoo's body_html email template field.

To fix this, use the QWeb-compatible t-out syntax instead. Here's how your email body should look:

<p>Dear <t t-out="object.partner_id.display_name" />,</p>

<p>Your subscription <t t-out="object.name" /> has been marked for renewal.</p>

<p>Please review your subscription details.</p>

<p>Thank you!</p>

This will ensure the actual values are rendered properly when the email is sent. Make sure your template is set to use QWeb and linked correctly in your automated action.

Hope it helps