Is there is a way to have the Total Amount Due to be included in the email to the customer just like having the invoice no using [Invoice No.]?

I understand the importance of having the Total Amount Due to be included in the email to the customer, FShah. I'd be glad to share insights about this. 

QuickBooks Online gives you the tools to create personalized and professional-looking invoices, estimates, and sales receipts. We can include the Total Amount due when emailing customers by customizing your sales form. 

Here's how:

1. Go to the Gear icon and then select Custom form styles.
2. Click  New style.
3. Select the Content tab, and tick the box beside Show on Invoice.

I'm adding the link below to guide you in recording customer payments for future reference: Record invoice payments in QuickBooks Online.

Keep your posts coming if you more assistance with customizing invoices in QBO. I'm always here to help. Have a great day. 

Thank you for the response. Unfortunately, the information that you shared is not what I was looking for. What I wanted to know was if there was a way to have the invoice amount due to show up in the "Message to Customer" section under the email tab. For example if I use  [Invoice No.] in the body of the message to the customer it displays the related invoice number. I was able to do that in Quickbooks desktop by using the [Transaction-Number] for the invoice number and [Transaction-Total] for Amount Due. Below is an example of what the email template was setup in QB Desktop and all the fields that it would be able to display in the message to the customer.

Dear [Name-First-Last]:

Your invoice-[Transaction-Number] for [Transaction-Total] is attached. Please remit payment at your earliest convenience.

Thank you for your business - we appreciate it very much.

Sincerely,
[Company-Name]

[Company-Telephone]
[Company-Website]

I hope that this helps. Thank you.