If there are no Tickets associated with an Opportunity record for a registration made through Soapbox Events, you may need to confirm that all Lead fields have been mapped properly from the Lead to the Opportunity object.
To do so, review the instructions in the article Install your Soapbox Engage for Salesforce Packages and take a particularly close look at the field mapping section of the Installation Instructions for Soapbox Events QuickStart and Soapbox Events for Salesforce document.
It may be that the Soapbox Registration Order Id isn't mapped from the Lead to the Opportunity. The packages look for that to move the Tickets over. If that's missing, other fields might have been missed in that list as well. Review each item in that list and update your Lead field mapping, as needed.