It worked fine in our UAT environment but is failing when we move to production
In UAT were you connected to your production instance of World-Check or a Pilot Instance of World-Check? 404 suggests that something is incorrect in the custom mapping which is preventing the case from being created in World-Check. If it worked fine in UAT then the most likely reason for this is that the Group ID you specified in production is incorrect. Group Ids are unique to each World-Check environment so please check the IDs from your production World-Check and then check the mapping in your custom flows/apex is referencing the correct ID.
There is information on how to find the group id on the developer portal.