First transaction not appearing in Transaction.updates

I have a StoreKit 2 transaction observer. I am making a purchase with StoreKit 1, by adding the payment to the SKPaymentQueue. I then want to listen to Transaction.updates to get details about the transaction. My listener looks like this:

final class TransactionObserver {
  private var updates: Task<Void, Never>?

  init(delegate: TransactionObserverDelegate) {
    updates = newTransactionObserverTask()
  }

  private func newTransactionObserverTask() -> Task<Void, Never> {
    Task(priority: .utility) { [weak self] in
      for await verificationResult in Transaction.updates {
        await self?.handle(updatedTransaction: verificationResult)
      }
    }
  }

  private func handle(updatedTransaction verificationResult: VerificationResult<Transaction>) async {
    ...
  }
}

For some reason, the handle(updatedTransaction:) function never gets called on the first transaction. Only on subsequent renewals. Why? Am I doing something wrong? Shouldn't this call the listener when the transaction completes?