My content is stored in S3 and we have limited access to it. We would prefer not to make this content public but are unsure what the domain or ip address ranges are for us to allow access for the Shotstack.io API. I looked at the support info and did not see it included there either.
If the content is stored in S3 then you do not need to make it publicly available. Instead you should use signed URL’s and provide us with the signed URL in your JSON or API request.
AWS has more details on how to share private objects with others using signed URL’s: Sharing an object with a presigned URL - Amazon Simple Storage Service.
The same would be the case for Google Cloud Storage: Signed URLs | Cloud Storage | Google Cloud
And Azure storage: Grant limited access to data with shared access signatures (SAS) - Azure Storage | Microsoft Docs