Hi there @VMDAEC, welcome to the Community!
Does Swoogo have an API endpoint that would allow you to update the registration to record the invoice number? If so, you could potentially use a Webhooks action to do that - Send webhooks in Zaps. Then, when your second Zap triggers for the cancelled registration that invoice number should be passed to the Zap as well, allowing you to reference it in the notification.
If not, perhaps you could create a lookup table in an app like Zapier Tables. The lookup table would essentially be a list of the registrations ID numbers and their corresponding QuickBooks invoice numbers, see: Create lookup tables in Zaps guide for more details. The first Zap would create the invoice and add a record to the table that includes the registration ID number and the invoice number. Then when the second Zap runs it would use a Find Record (Zapier Tables) action to search for a record with an ID number that matches the canceled registration’s ID number, which would get the corresponding invoice number to be used in the action that sends out the notification.
Hope that helps to get you pointed in the right direction. If you run into any issues on that or have further questions just let us know!