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If you're working on new template in separate directory under /templates [ex. /templates/myintegration/ ]dir you don't need to change your current template just to preview your changes. You can add &systemtemplate=myintegration param to url just to change current template for your session. Note: You need to be logged in as administrator to do this.
Debugging template
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When you've made mistake in Smarty syntax you wont be able to see your template (it will render blank) - you can enable error reporting in /includes/config.php file of your HostBill to locate where error has been made.
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