One essential feature within WHMCS is the automated emails it sends.
These emails range from invoice reminders, ticket notifications, and service suspensions and so on.
Please follow below mentioned steps
Step 1: Creating a new email template
Login to your WHMCS admin area and navigate to: Setup -> Email Templates
Find an existing email template associated with a product and click on the Edit icon.
Copy the content of the email template and go back to Setup -> Email Templates
Under Create New Email Template click Product/Service and enter a unique name you’ll be able to easily associate this template with
Paste the content you copied above and make your desired changes
Enter a name for the email template subject and click on Save Changes
Step 2: Assigning the email template
Whilst still in your WHMCS admin area navigate to Setup -> Product/Services -> Products/Services
Find the product you would like to assign your new email template to and click Edit
Under the Details tab find your new email template and click on Save Changes