With regards to the green dot notification of opened un opened invoices , this seams to be very random, as most of the time it never shows as open , but he invoices get paid . so they must be seen. Is there a setting somewhere that I’ve missed?
By default the amount is in the email template so if they know what the invoice is for and you haven’t modified the template then they are probably just paying it without clicking the link.
Are you attaching the invoices to your emails as PDFs? If so, your customers will simply print the pdf attachment instead of clicking the link in the email.