To receive the recurringDetailReference token synchronously in the payments response, you should enable this in the Additional Data Settings. Please follow the steps described in our docs here: Receive recurringDetailReference in payments response.
Once this is set up, we will include the token in the synchronous response when it is available. Sometimes, the token is available asynchronously only meaning it will not be present in the API response. In those cases, we recommend to rely on the RECURRING_CONTRACT webhook or to make a /paymentMethods call to retrieve the token.