Create a new tax registration order for an employer across one or more US states.

About apiUserPid: this is your partner identifier issued by CorpNet during onboarding. The Tax Registration API and the Business Formation API may issue different apiUserPid values to the same partner — a value that works for one API may be rejected by the other. If you receive 400 "Please Enter a valid value for APIUserPid", contact your CorpNet account manager to confirm the value for this API.

About pcid: this is your own customer identifier (Partner Customer ID). The API does not enforce uniqueness — submitting the same pcid twice produces two separate orders with different orderGuids. Idempotency and deduplication are the partner's responsibility.

On success, returns HTTP 201 with the full submitted order echoed back, plus computed identifiers (id, orderGuid) and empty arrays for accountNumbers, taxRates, and agencyAccounts (which populate as the order progresses through fulfillment).