Steps to reproduce:

• use FishEye or Crucible 4.3.0 or later
• in the installer wizard paste the Atlassian Stack license key
• FishEye installer rejects the key with a message "You've entered a Crucible license"
• Crucible installer rejects the key with a message "You've entered a FishEye license"

Workaround:

• in the installer wizard use an evaluation key
• after FishEye or Crucible is installed, navigate to Administration > System Settings > System Info > License > Edit license
• paste the same Atlassian Stack license key into "FishEye" and "Crucible" input fields