There are two ways this can be done, check out the managers article here for a better explanation.
No, unfortunately this isn't possible at the moment. However, you can remind people who haven't activated their profile yet to download the app and login via an e-mail.
Navigate to your programme item.
Tap the menu icon (top right for IOS, bottom right for Android).
Click on 'Scan participants'.
Scan the participant's QR code (If they shake their phone with the app open, their QR code will pop-up).
Dependant on the scan settings, a person may or may not be allowed in the relevant program item. The app indicates whether the Workshop is full, or if that they can enter.