The payee shares its tax information with this payer, against the payee's own Payer relationship record. Sharing is a standing, ongoing grant: the payee's current active ComplianceEntity and every future one is shared, and each automatically projects a certified Auto W-9 into the payer's Forms when Tax-verified. Grantor-session-only: the payee's own session must grant consent; any supplied X-Wingspan-Account acting-as header is rejected 403 before any service call. Foreign or missing ComplianceEntity ids return a uniform 422 with detailCode: users.ComplianceEntityNotOwnedByGrantor. Idempotent via Idempotency-Key. Fires Payer.TaxInformationShared.