Calling the new 'Custom API' feature from within a Custom Widget
From what I've learned it is not possible to call an endpoint from the new "Custom API" feature within a Creator Widget. The SDK's doesn't support it yet, when calling it natively you end up with CORS issues or at least I couldn't get it working even with proxies.
I think this is a crucial feature to use the Custom API not only from third-party apps, but certainly from widgets within Zoho too! This allows you to combine multiple calls into one and simplifies the logic in such custom widgets immensely.