Contact your service administrator (your software vendor; or Nexetic Support team if you purchased the service directly from us). They will be able to send you a new invitation email.
In case you know your username for Nexetic Shield Win + Mac, you can just use the download links below.
Download link for Windows: https://shield.nexetic.com/installers/NexeticShieldInstaller.msi
Download link for OS X: https://shield.nexetic.com/installers/NexeticShield.dmg
After completing installation and moving into Guided Set-Up phase, fill in your username and then click Forgot your password? link to obtain a new password via email.
With your existing username and new password you can complete the activation of the client application.