The hirer says the link won't open
Work out whether it's the hirer's browser, a link that has closed, or an email that never arrived, and what to do about each.
Three different problems all show up as "the link won't open", and each needs a different fix. Work through them in order.
The browser or device
Ask what they opened it on. A very old phone browser, or a browser with JavaScript switched off, will fail to load it. Ask them to try a recent Chrome, Safari, Edge or Firefox, on a phone or a computer. It is still the same link: nothing needs to be resent for this one.
The link itself has closed
The link stays live for the whole hire and for 30 days after it ends, and it stops early if the booking is cancelled or if someone has used Revoke link on it. Open the booking and check its dates and status: a hire that ended more than 30 days ago, or a booking marked cancelled, will not accept a check-in any more, however the link was sent.
If that is what happened, open the booking's Hirer link section and use Send new link. It always mints a fresh link and kills the old one in the same step, whether or not you had sent the first one, so you never have to revoke first.
The email never reached them
Send new link tells you plainly whether the email went out. If it says the email did not send, or that there is no address on the booking, KeyProof cannot get it there by email at all: copy the new link with Copy link and send it yourself over WhatsApp or text instead of waiting on the inbox.
There is no delivery log to search for a bounce or a spam flag. If you are not sure an email reached someone, send the link over WhatsApp as well rather than resending the same email and hoping.