API returning 500 on nested custom field expansion

Question

Getting consistent 500s when trying to expand custom fields on /work_orders . Request works fine without expansion. 
 GET /v1/work_orders?expand=custom_fields.customer_preferences&limit=50 
 Response: 
 HTTP/1.1 500 Internal Server Error
{"error": "internal_server_error", "request_id": "req_7a8f9e2d1c4b"} 
 Works: 
 GET /v1/work_orders?expand=assignee,customer&limit=50 
 Same behavior on jobs endpoint. Custom fields exist and are populated in UI. 
 req_7a8f9e2d1c4b, req_8b3c0a5f2e9d, req_9d1e4f7a3b8c — all from last 2 hours.

Eli Torres (Staff) · Accepted Answer

Comma-separated string: 
 GET /v1/work_orders?expand=custom_fields&custom_field_ids=cf_123,cf_456&limit=50 
 You'll still need expand=custom_fields — the filter just limits which keys come back in that object. 
 Heads up: custom_field_ids without expand=custom_fields is silently ignored right now. Another rough edge for the cleanup list.

Leo Nakamura · Answer

Docs are wrong here: help-055 shows dot notation for custom field expansion. Should be deprecated or corrected. 
 Also — expand=custom_fields.customer_preferences was valid in v1.0-v1.1. Breaking change not listed in news-025.

Devon Marsh · Answer

Running into something similar. custom_field_ids filter works, but there's a gotcha with deleted fields — if you include a deleted field ID, the whole request 500s instead of returning null or omitting it. 
 Workaround is to fetch /v1/custom_fields first and validate IDs against active ones. YMMV.