Authenticate to Finch with a token that has pay:deductions:write scope for the employer
GET /employer/benefits to retrieve existing benefit deduction IDs and confirm the 401k benefit is already registered
POST /employer/benefits/{benefit_id}/individuals to enroll or update an employee's contribution rate, specifying employee_deduction amount and type (fixed or percent)
Handle the async job response by polling the returned job_id via GET /jobs/{job_id} until status is complete
Reconcile the applied contribution rates against the recordkeeper's expected values after the next payroll run to verify end-to-end consistency
Known gotchas
Finch's deduction write support is provider-dependent; check the provider capability map for pay:deductions:write before attempting writes to avoid silent no-ops
Some payroll providers batch deduction changes and only apply them at the start of the next pay period; real-time confirmation does not guarantee the current payroll cycle picks up the change
Percent-based vs. flat-dollar contribution types are represented differently across providers even through the unified API; validate the type field against provider-specific behavior
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