extract_transaction_id_from_app_receipt returns None where legacy endpoint return valid transactionId

[marcuseckert]

So, it looks like the extract_transaction_id_from_app_receipt return None for some receipts. I wonder if it has to do with the fact that the receipt I've tested only contains a freeTrial. Calling the verifyReceipt endpoint resolves the exact same receipt properly and also managed to give back a transaction id.
I'd appreciate any advice. It's a user's receipt so I don't want to post it here.