This is usually caused by forgetting to scan the ID. If the session is still open, scan the correct IDs now. If the session is closed, you can use the reassign tool in the Admin Gallery in the Console to add/change IDs attached to any images.
If using Facial Recognition
Is the person registered properly?
If you are using Facial Recognition, it is possible that the customer has not registered for this specific event (maybe they had the wrong link?), or that the selfie they supplied was low quality (eg bright light behind the head so facial features aren't discernable). Give the customer the correct link to register for this Event and ask them to register their selfie again. That should sort it out.
Have the images not been processed for some reason?
If it's still not working, double check that the Event has Facial Rec enabled and that all images have been processed by the facial recognition integration. Go the Event Page, Select the Integrations tab and then click details on the Facial Recognition Integration - if you have unprocessed images, you should close that window and then select the sync function in the upped left of the Facial Recognition integration tile.