Co-founder and CTO of HelloSign here. Sorry to hear that OP's bug reports weren't taken seriously. Good tech support is a must for mission critical APIs. At HelloSign we take great pride in our API and our tech support. Rather than outsource support or rely on less technical people, we have our developers directly support the API they built. So when you give our API a try, I encourage you to check in with one of our…
Highly recommended, and we've been with them for 2+ years!
Disclaimer - Never used the API, just like the service and its Box integration