If you have transactional templates you want to use with handlebars syntax, you need to migrate your legacy templates to the new dynamic templates page.
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The original template you copy won't be modified and remains active in any API or SMTP calls. To use the new template, update the template ID parameter in your code.
Create a version of the template you wish to migrate or select the actions menu on the template version and select Edit. The template opens in the editor and a green banner appears at the top of the page specifying that the template you are editing is a legacy template.
Select Copy as New Template.
Give the template a new name and click Copy as New Template.
Once the template is successfully copied over, click Continue. The template opens in the editor and you are prompted to replace any existing substitution tags with handlebars syntax.
To replace any existing substitution tags, click Replace your substitution tags.
Enter the opening and closing characters of your substitution tags and click Replace.
The module replaces all of the substitution tags in your template with handlebars.
For example,{{your_tag_here}}.