Rodrigo has a custom code action that generates a URL and outputs it as 'reviewLink'. He wants to use this output directly in a subsequent 'Send email' action's body like `{{custom_code.reviewLink}}`.

Justin Givens explains that custom code outputs cannot be directly inserted into email templates 'on the fly'. The correct method is to add a 'Set property value' action after the custom code action. Use this action to copy the 'reviewLink' output from the custom code into a custom contact property. Then, use the personalization token for that contact property within the email template.