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PCs & shop network

The tills' certificate

How tills on other PCs recognise the store PC, how BooksPOS changes that certificate without pairing again, and what to do if a till missed it.

Tills on other PCs talk to the store PC over an encrypted connection. They recognise the store PC by its certificate: when a till is paired, it remembers that certificate's fingerprint and refuses any other PC that claims to be the store PC. From time to time the certificate has to change. BooksPOS does that without pairing every till again. This guide explains how, how to change it yourself, and what a till that missed the change shows.

Where to see it

On the store PC, open Staff & counters. The Tills on other PCs card shows:

  • the certificate's fingerprint (the first 16 characters, in groups of four) and the date it is valid until;
  • while a change is under way, the new certificate and when it will be used at the latest;
  • for each till: when it was last seen, its BooksPOS version, and whether it has the new certificate or missed a change.

How the certificate changes

  1. Announced ahead of time. Sixty days before the certificate expires, the store PC makes the next one. Each till learns it within minutes, over the connection it already trusts, keeps it as a second fingerprint, and confirms it to the store PC.
  2. Used once every till has it. The store PC switches to the new certificate as soon as every paired till has confirmed it, and at the latest after 30 days. Nothing restarts, and nobody types a code.
  3. The old one kept for stragglers. For 30 days after the switch, a till that was switched off and did not learn the new certificate is still shown the old one at the address it last used, so it can learn the new one when it comes back. After that the old certificate is deleted.

New certificates are valid for three years. The dashboard and the bell say when a change is under way, when the certificate is close to its expiry, and when a till missed a change.

Change it now

An owner can change the certificate at once, for example when a PC that was paired as a till has left the shop:

  1. On the store PC, open Staff & counters.
  2. Choose Rotate now under the certificate, and confirm.

The new certificate is announced to the tills at once and used as soon as they all have it, within the hour at the latest. If a till's pairing should end as well, choose Remove next to it.

A till that missed the change

A till never trusts a certificate it was not told about: that is what stops another PC on the network pretending to be the store PC. A till that was switched off for the whole change, or got a new network address, therefore stops connecting and says:

"The store PC's security certificate changed while this till was away, so this till does not trust it any more. Pair it again."

To pair it again:

  1. On the store PC, open Staff & counters and choose Add a till. Note the address and the code.
  2. On the till, the Connect to the store PC screen is already open. Type the address and the code.

The till keeps its printer settings and any bill in progress. On Staff & counters the store PC marks such a till as having missed the change until it is paired again.

Common questions

Do I have to do anything when the certificate changes by itself?

No. The certificate changes by itself, and switched-on tills follow within minutes. Only a till that stays off for the whole change needs to be paired again.

Why not simply accept the new certificate?

Because a PC that pretends to be the store PC would show a new certificate too. A till accepts only a certificate it learnt from the real store PC over the connection it already trusted.

Does a replacement store PC keep the certificate?

No. The certificate belongs to the PC. After a store PC is replaced and its backup restored, pair every till again.

Last updated 30 September 2026. Still stuck? Contact us.