Declining to sign
Nobody has to sign electronically, and saying no is a normal thing to do.
Choose Decline to sign from the invitation or signing screen.
Declining provides an optional reason and asks for confirmation. Screenshots use a demonstration workspace. Optionally enter a reason, then confirm the decline.
You should see
The sender is notified and the request closes. Other outstanding invitations and reminders stop.
If it did not work
A decline cannot be undone. Ask the sender for a new request if it was a mistake.
If you prefer to sign on paper, discuss that alternative with the sender.