Written for Synergy 1 (v1.21.4), checked 7 October 2026.
Enter your serial key on every computer in your setup. Only the server uses an activation, but each computer needs the key. Copy it from your Synergy 1 or Synergy Business license on your account page: Your account
Enter or change your serial key
- In Synergy 1, choose License > Change serial key.
- Paste the key into Enter your serial key.
- Click OK.
You can also open the same window from Help > About Synergy... (on macOS, Synergy > About Synergy), with Change next to your key.
Synergy 1 confirms with Thanks for entering your serial key and the edition, which also appears in the window title. Do this on every computer, with the same key: with encryption on, Synergy 1 reminds you that using the same key everywhere keeps TLS working.
Entering the key doesn't activate it. Your license activates on the server the next time you click Start. How activation works, including offline keys: How license activation works in Synergy 1 and Synergy 3
After an upgrade or a trial
Enter your new serial key on every computer, as above. An upgrade (for example from Synergy 1 Basic to Synergy 1 Pro), or a Synergy Business trial turning into a paid business subscription, puts a new serial key on your account, and Synergy 1 doesn't download it for you. A trial key stops working when the trial ends; if it already has, the Serial key window opens by itself when Synergy 1 starts.
Synergy 1 Pro adds TLS encryption. If it isn't on after you upgrade, turn it on, on every computer. For the steps, see: Encryption and fingerprints in Synergy 1
The first time you open Synergy 1
The Serial key window opens by itself when Synergy 1 has no valid key, and again if you click Start without one. Its links take you to your account page, to Purchase a license, or to Request an offline key for computers without internet access. If you click Cancel, Synergy 1 explains that you need a license and closes when you click Exit; click Back there to go back and enter a key.
When your license or trial is ending
Renew your business subscription, or buy a license when your trial ends, then enter your new serial key in the window that follows the warning. Once the license has expired, Synergy 1 stops working until you enter a valid key.
Synergy 1 warns you before a business subscription or trial ends, for example with Your license expires in 3 days or Your trial ends in 3 days, and again once it has ended, with Your license has expired or Your trial has ended.
If your key isn't accepted
- Invalid serial key. Copy the whole serial key of your Synergy 1 or Synergy Business license (not a Synergy 3 one) from your account page and paste it in. On Synergy 1 (v1.17 and earlier) that won't help, so update instead: Older Synergy 1 says Invalid serial key?
- Sorry, that serial key has expired. Renew your license, then enter the new key.
- The settings file is not writable. Ask your administrator, or check the permissions of the file named in the message. Synergy 1 can't save your key until it can write to that file.
Older Synergy 1 says Invalid serial key?
Update to the latest Synergy 1, then enter your key again. For the download, see: Download Synergy 1 or Synergy 3, including older versions
Synergy 1 (v1.17 and earlier) can't read our newer serial keys, so it rejects a valid one. To check your version, see: Find which version of Synergy 1 or Synergy 3 you're running
Can't update, for example because the latest Synergy 1 doesn't run on your operating system?
- For business and enterprise customers: on Synergy Business Advanced or Synergy Enterprise, we build the latest Synergy 1 for any system its vendor still supports, paid extended support included. Otherwise, we'll send you a serial key your version reads. To ask for a build or a key: Contact our business team
- For personal, non-commercial customers: contact us and we'll send you a serial key your version reads: Contact support
Which systems the latest Synergy 1 runs on: Operating system and hardware requirements
What each older version shows:
- Synergy 1 (v1.17): Invalid serial key. Please contact us for help. Newer versions show the same message for a mistyped key, so check your version first.
- Synergy 1 (v1.15 and v1.16): Sorry, a fatal error has occurred and the application must now exit. The error under it mentions invalid serial key version, and Synergy 1 closes when you click Abort.
- Synergy 1 (v1.8.5 to v1.14.6): An error occurred while trying to activate Synergy. The message ends with Invalid serial key.
Using Synergy 3? See: Enter or change your serial key in Synergy 3