I’ve tested adding the signature on both quotes and invoices.
It works perfectly on quotes.
However, I can’t find any place to sign the invoice after receiving the invoice email sent by Invoice Ninja system.
I can see the approve button when I click the quote link to the client portal. After clicking the approve button, it will pop out a window to let me sign. But I can only see the “Download PDF” button on invoice. There is no other button or place that can let me sign the invoice.