The short answer
Every KYC link is single-use and stays valid for 14 days from the moment you send it.
What single-use means
The link works until the contact finishes the form. Once they fill it in, sign it, and submit, the link stops working. It cannot be opened or reused again. At that point their status turns to Submitted and the signed PDF comes back to you on the company's KYC tab.
Because a link is single-use, you cannot use one link to collect two people's details. KYC is per contact, so each person gets their own link.
What 14 days means
The link expires 14 days after you send it. If the contact has not finished within those 14 days, the link goes dead. When they try to open an expired link, they see a page telling them the link is no longer valid. Nothing they typed before is lost from your side, because a form only reaches you once they submit.
When the clock resets
Each time you resend, IzzyTap makes a brand new link and starts a fresh 14 days. The old link stops working straight away, so only the newest link will open. See resend a KYC form and refresh the link.
Tip
If a contact says their link has expired or will not open, you do not need to do anything clever. Just resend from the company's KYC tab to give them a working link and a fresh two weeks.
If a link has already lapsed
A lapsed or already-used link cannot be revived. Send again to issue a new one. For the full troubleshooting steps, see fix a KYC link a contact says won't open.