Validates the configuration on an instance. This includes checking any API keys to 3rd party APIs. Returning success signals that the configuration values are all correct and valid. Validation should return groups of related validation errors. If there are values that are out of range, it should return only those fields with appropriate code. Additionally, if other API keys are invalid, those should not be returned along with other invalid fields. It can be called at any time after the app installation (including also the process of installation, but after the lifetime event has been sent). Also, it can be called even if the app doesn't have any configuration settings declared.

The endpoint is available for descriptor versions 1.1 and above.