purchaseBelongsToOtherUser (error code 40): Purchase belongs to another user

• The backend answered 7852 (purchase belongs to another user). The iOS SDK maps it here, and returns it as the purchaseBelongsToOtherUser result in the Swift async API (BackendErrorCode.swift).
• The link was opened on a device signed in as a different app user than the first one that redeemed it.
• A link was shared with another person, or forwarded, and they redeemed it first.
• Android maps 7852 to ProductAlreadyPurchasedError and has no member for this code (errors.kt).

• Do not retry. The purchase is bound to the first user.
• Tell the customer that the purchase belongs to another account, and offer support. Do not name the account.
• Do not grant access from the error.

// Swift
do {
  let result = try await Purchases.shared.purchase(package: package)
} catch let error as ErrorCode where error == .purchaseBelongsToOtherUser {
  // handle purchase belongs to another user
}

On RevenueDot: RevenueDot claims the purchase before it moves anything, so of two simultaneous redeems exactly one wins. The other gets HTTP 400 with code 7852, unless it is the same app user ID retrying, which gets the same customer back.