How to get the saved cardIdentifier in opayo pi?

Question

I am doing back end developing for payments using opayo pi https://developer-eu.elavon.com/docs/opayo

I have a doubt. In docs they said, we need to create a cardIdentifier before making transaction . see this. https://developer-eu.elavon.com/docs/opayo/spec/api-reference-0#tag/Card-Identifiers

And we can make it a card as a reusable card by "save": true when create a transaction. https://developer-eu.elavon.com/docs/opayo/tokens-reusable-identifiers#reusing-the-token https://developer-eu.elavon.com/docs/opayo/spec/api-reference-0#operation/createTransaction

and, next time when we can use it by giving only cvv(securityCode) . we do not need to give the card details such as cardholderName, cardNumber, expiryDate.

And they said,

If you are using a reusable card identifier and require a security code check, you will need to link the reusable card identifier with the security code.

see here https://developer-eu.elavon.com/docs/opayo/spec/api-reference-0#operation/linkCi.

My question is,

How we know it is a reusable card,and how to get the cardIdentifier( which is already saved) without sending card details. because The POST request for Link a Card Identifier is https://pi-test.sagepay.com/api/v1/card-identifiers/{cardIdentifier}/security-code so e need the value of {cardIdentifier}.

If is there anyone working this API, Please clear my doubt.