Read and write employee custom field data and org-hierarchy attributes via the Merge HRIS passthrough API for a provider not fully supported by unified endpoints
Identify the target HRIS provider's native API endpoint and request structure for the custom field or org attribute you need to read or write
POST /hris/v1/passthrough with the method, path, headers, and body matching the native provider API call
Parse the raw provider response returned in the data field of the passthrough response, applying provider-specific field mapping
For writes, construct the native provider request body and POST it via passthrough, then verify the change by re-reading the record
Wrap passthrough calls in a provider-specific adapter layer so the upstream application remains insulated from provider API changes
Known gotchas
Passthrough requests count against both Merge API rate limits and the underlying provider's own rate limits; high-frequency passthrough calls can exhaust provider quotas
Merge does not validate or transform passthrough request/response bodies; malformed native API requests will fail with provider-specific error codes that must be mapped manually
Passthrough is intended as an escape hatch for unsupported fields; Merge may add native support for previously passthrough-only fields in future versions, so review the Merge changelog periodically
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