I think you mean the App ID. The app ID of your project can be found in the developer portal when you go to the project and then ‘general’ under ‘settings’
After clicking it you'll see this text (somewhere near the bottom):
and then there is a long string in a grey block
Dear Ayah,
If you are not running in the cloud, an on-premise license required https://docs.mendix.com/developerportal/deploy/licensing-apps-outside-mxcloud
Therefor you need the server ID
Or
https://docs.mendix.com/developerportal/deploy/unix-like#3-license-key-activation-on-linux
Please contact support to request a license for your Server ID
Cheers, Andries