Re: Custom properties
Hi @kevburt ! Welcome to the Zuora family. We have some exciting projects in the hopper for developers right now so it's an exciting time to join!
Anytime you see a "__c" that means it's a custom field. You can check out all the custom fields defined in your Zuora tenant via these instructions: https://knowledgecenter.zuora.com/BB_Introducing_Z_Business/Manage_Custom_Fields
We also have a nifty new Settings API that you might want to check out too. It's still "in development" but we've pushed what we have so far to most Zuora tenants so early adopters can check it out if they want to. I don't think Custom Field settings are exposed in that quite yet, but I believe there are plans to add that in the future. @kurtlu, the product manager, can confirm or deny.