Normally Guest Count and Event Type will show on your quotes but not your invoices.

If you would like this information to show on all of your future projects, you can enable this option from your Account Settings.

To access these settings, click your name in the top right and select 'Account'

From here click 'Settings'

Now scroll down to Contracts and enable Event Type and Head Count information on Contracts

This will apply to all projects that you create moving forward.

If you'd like to adjust it on a current project you can click the 'Gear' symbol on the project.