Visit your AdGuard personal account, there you can reset your license and enter the key again.
But this is a pretty strange problem, so I would like to ask you for more information.
Please, export the logs and send me the received archive in PM.
It is also advisable to specify an approximate time of what happened.
Do you remember under what circumstances the license was dropped? Maybe after a Windows update, installation of new applications, or something like that.
This information would be very helpful in solving the issue.
I have bought a new pc and by reinstalling adguard it has ask for the licence key, by filling in the key it says ''Key is not valid'', I am sending this with my laptop were Adguard is still working, I have a private network with 3 computer on it and never had a problem
The behavior you described happens when your license key hits the maximum amount of concurrent activations available to you. This can happen if you have reset the device to factory settings or installed AdGuard on a new device. There's no need to purchase a new license - just reset your key in order to reactivate it.