1. Open System Settings and Email Templates. Find the exact message type that the relevant event sends.
2. Save a copy of the current subject and body before editing.
3. Write a concise explanation, action link and product-specific guidance. Use the merge fields listed for that template type.
4. Review sender information, attachments and any CC or BCC recipients where those controls are available.
5. Update the intended language variants as well as the default.
6. Send a controlled example using representative data, then check the rendered HTML, plain-text readability and links.

A product email and an invoice email do not expose identical merge fields. Test optional values and conditional branches with both present and missing data. Link to relevant knowledgebase instructions instead of embedding an entire long setup manual in every welcome message.

WHMCS 9.0 removes support for legacy Smarty constructs. Keep application logic in supported hooks or modules and use the resulting safe merge fields in the template.

Use a Product email template where the merge-field list confirms {$service_custom_field_websitepurpose}. This example assumes you created the Website purpose product field described in the custom-field guide. In HTML view, the optional line can be written as:

{if $service_custom_field_websitepurpose}
<p style="margin:0 0 12px;">
  Website purpose:
  {$service_custom_field_websitepurpose|escape:'html':'UTF-8':false}
</p>
{/if}
<p style="margin:0;">You can review this service in your client area.</p>

The condition omits the label when the field is empty. The escape modifier treats the value as HTML text. The final paragraph remains in either case.

Test both paths: send one authorised test with Business website selected and another with an empty optional field. Confirm readable output and no unexpanded Smarty text. Keep the existing global header/footer and any required support-ticket subject structure. Do not assume this Product field is available in every Invoice, Domain or Support template.

• Configure authenticated outgoing email in WHMCS
• Investigate missing WHMCS client emails
• Organize and maintain a WHMCS knowledgebase
• Maintain a custom WHMCS theme across upgrades

• WHMCS email templates
• WHMCS 9.0 release notes
• WHMCS knowledgebase
• WHMCS order form templates

• Smarty HTML escape modifier