You’re absolutely right: the issue is caused by the End Call node being created with an empty server.credentialId, and the validator expects a UUID even when no server is actually required. So as soon as the End Call node exists (even in an empty workflow), saving fails because credentialId: is invalid. This is clearly a platform bug, not a configuration mistake on your side. I can help by reproducing it cleanly and then suggesting a practical workaround (for example, resetting or re-binding the node so it generates a valid UUID, or bypassing the validation until the vendor patches it). If you want, I can also help you prepare a clear bug report for the platform team with exact repro steps. @