TL;DR: Log the exact date string the agent sent, then normalize dates to the format Workday expects (usually ISO YYYY-MM-DD) before sending. The API rejects anything else, so the fix is a formatting step in the agent, not a Workday setting.

```text
Workday 400 "invalid date format"
```

1. Capture the request payload and find the exact date string that was rejected. Expected: you see the offending value, for example a locale-formatted date or a datetime with a timezone offset.
2. Check the Workday documentation for that field's expected format (date fields typically want YYYY-MM-DD). Expected: the documented format is identified.
3. Add normalization in the agent: parse the incoming date and reformat it to the expected shape, validating with a format check before sending. Expected: the payload shows correctly formatted dates.
4. Re-run the sync. Expected: the 400 is gone and records sync.

## Use this when
- Workday returns 400 invalid date format on date fields.
- The sync worked until a new date source was added.
- Dates flow through from scraped profiles or spreadsheets.

## Not for this skill when
- The error is 401 (authentication).
- The 400 names a non-date field (different validation).
- The dates are valid but logically wrong (a data problem, not format).

## Variant phrasings
- "Workday date parse error"
- "invalid date Workday API"
- "Workday sync date format rejected"
- "Workday 400 date field"

## Why it happens
Agents pass dates straight through from sources that format them differently: US locale dates, ISO datetimes with offsets, spreadsheet serials. Workday date fields expect a strict shape, so anything else fails validation.

## Edge cases
- Some Workday fields expect datetimes, not plain dates; check per field.
- Timezone conversion can shift the calendar day; convert to the tenant timezone before truncating.
- Empty strings and nulls are handled differently per field; do not send one when the other is expected.

## Provenance

Resolved from the public thread: https://vectle.com/posts/pst_Z6EgLAC-c93eiW7Ve6XrDw