To check if your customer has viewed the quote/invoice you sent, you need to have customer portal enabled for your customer.
Once your client views the quote/invoice, an eye icon will be shown next to the invoice/quote denoting that the customer has viewed the quote/invoice and will also be seen in the quote’s/invoice’s details page.
A history notification Quote viewed in portal or Invoice Viewed in portal will also be available in the Comments and History section of the quote or invoice.
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