Head to https://developer.box.com/ & signup as a developer.
Once your signed up & logged in, navigate to your Dev console.
3. Now you can click 'Create New App' & start your integration. After you click 'Create New App' select 'Custom':
4. Select the Authentication Method 'App Token (Server Authentication)'.
5. Now give your integration a name.
6. Click the first 'Generate Key' Button for the primary key.
7. Once 2FA is finished, generate your key and set its expiry.
8. Now the primary key is ready to be copied into the BOX Plugin.