Troubleshooting

Problem	Likely cause	Fix
Missing container	querySelector returned null.	Check the selector and mount after the element exists.
Missing transport	mountForm needs a submit path.	Pass transport.
Invalid transport config	transport.submit is missing or invalid.	Pass an object with submit(request) or use createJsonTransport(...).
Backend returned non-JSON	Default parser expects JSON.	Return JSON or use createJsonTransport({ parse }).
Unknown field kind	Registry does not include the field.	Use built-ins or register a custom field.
Unknown report kind	Registry does not include the report.	Use classifier, regressor, or register a custom report.
Duplicate id	Two fields or reports share an explicit id.	Give each item a stable unique id.
Custom element name invalid	Custom renderer tag lacks a hyphen.	Use a valid custom element name such as risk-band-field.
Form not updating after remount	Host reused stale schema/state.	Keep schema creation intentional and unmount on route changes.
Styles not inherited	Design system uses its own mode.	Use mode: "inherit" or override tokens at the container.

Start with the browser console and the network tab. Most integration failures are either schema validation, missing DOM container, or backend response shape.