Get a value from custom field in inventory into an email of Zoho Books

Get a value from custom field in inventory into an email of Zoho Books

Hello,

When I create an invoice (Zoho Books) there is an automated email sent to my customer based on a specific date.

This email shall contain a field content which is set up as a custom field in the product itself.
How can I get the value from that custom field into my email? Because I don't see such placeholder or variables when I create the email template.

I tried this: ${inventory.cf_check_in_link}

I'm not sure if this can work? Is there an overview on the variable which are accessible on all Zoho apps?

Best, Enrico