After a completed app transfer (accepted 2026-08-27), the recipient team's exchange of Sign in with Apple transfer identifiers fails with {"error":"invalid_request"} for ALL 159 identifiers, while the sending team can still regenerate the identical identifiers. A live login by a migrated user also returns an identity token without the transfer_sub claim, within the 60-day window. We followed TN3159 (identifiers generated before initiating the transfer) and verified our requests against TN3107; negative controls show our credentials pass validation and that genuine identifiers behave identically to nonexistent ones on the recipient side. Filed as FB24615867 with full request/response captures and long-lived client secrets for both teams, per the "Gathering required information" post. Team A: D2LZFX93J6, Team B: 3LQD4L73TY, App Store ID 6748244383.