Invite anybody who helps run the club, or generate a player link for a box. Everybody who runs the club is invited with an email address: it becomes their permanent sign-in. If you would rather hand the link over yourself, press Just give me the link and nothing is sent. Either way the link is not a sign-in. Opening it tells them what job they have been given and asks them to confirm their address, and the six-digit code that arrives is what puts them in.
If the person is already on your club list, pick them from Who is it rather than typing their name. That points their sign-in at the person you already have, instead of putting a second version of them on the register.
Never got it? Press Resend invite on their row. The same invitation goes out again and the link is shown here to copy, so you can send it another way if email is the part that is failing. Any earlier link stops working, and they stay the one person you already have on the club list.
Why it is never a link that signs them in
A staff sign-in can change your club: build a season, move people between boxes, read the register, in some cases see the money. A link that signed somebody in would be a link that does all of that for whoever else has seen it, and links get forwarded. So the invitation only says what job you are being offered, and the code that arrives at your own address is what proves it is you.
Nothing to think up and nothing to install. The code is six digits, it arrives in a few seconds, and from then on that address is how you get in on any phone or laptop.
One person, more than one job
At a real club the treasurer is often on the committee, and the person who runs the boxes is often the secretary. So somebody can hold more than one of the jobs at once: tick each one they do and they get everything all of them allow. Nothing is lost by giving somebody a second job, and taking one away leaves the others alone.
Up to 15 people can help run your club, on every plan, free included. None of them counts towards the members your plan holds. Who may do what is on Who does what.
Taking somebody off
People leave a committee every year and that is an ordinary thing rather than an incident. You can sign somebody out of their phones without removing them, which is what to do when a device goes missing. Or revoke them outright, which ends the job and the sign-in with it.
Nothing they did disappears. The seasons they built, the scores they entered and the trail of who changed what all stay exactly as they are, because it is the club's record rather than theirs.