The following wildcards can be used in email subjects, heading and content:
{site_title} : Site Title
{name} : Customer's full name
{first_name} : Customer's first name
{last_name} : Customer's last name
{email} : Customer's email address
{invoice_number} : The invoice number
{invoice_currency} : The invoice currency
{invoice_total} : The invoice total
{invoice_link} : The invoice link
{invoice_pay_link} : The payment link
{invoice_receipt_link} : The receipt link
{invoice_date} : The date the invoice was created
{invoice_due_date} : The date the invoice is due
{date} : Today's date.
{is_was} : If due date of invoice is past, displays "was" otherwise displays "is"
{invoice_label} : Invoices/quotes singular name. Ex: Invoice/Quote
{invoice_quote} : Invoices/quotes singular name in small letters. Ex: invoice/quote
{invoice_description} : The description of the invoice
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