It sounds like you were trying to click on an expired signature link. This happens when you open a signature request and view the document on one device, browser or IP address, but do not complete the request on that same device, browser or IP address. When you try to re-access the link again from another device, you would receive a message saying the link is no longer valid.
To resolve this, simply click on the button to "request a new link" and make sure you both view and complete signing the signature request on the same device, IP address or browser.
