I am a developer looking into building an integration with CaptionSync

You need to first create a CaptionSync developer account. Under Type of Account select Web captions, and under Organization name put the name of your organization, with Test Account in parentheses (e.g., My Company (Test Account)). You will receive an email response with the username and login info.
Then log into the Support Center to open a Support ticket, and request that we give you access to our API documentation. You can also include additional information about your workflow so that we can advise you further and help you with any questions you have.