How do I validate purchases on the backend using getPurchase?

In the docs of https://www.revenuecat.com/docs/api-v2#tag/Purchase, it requires purchaseId which seems to be missing from the react native SDK?

I have tried using both transactionIds in customer info and in the transaction object but it the api fails to return so. Is this because the IDs are only in sandbox/test purchases in Android?

Using the get all https://www.revenuecat.com/docs/api-v2#tag/Customer/operation/list-subscriptions is less than ideal when one user has multiple purchases.