Flutter entering to sub-sub collection in firebase

my nested collections looks like this:

User--> drugs--> drugsTime

I want to update data in document in the subsub-collection (drugsTime)
however I dont know the drug document id and the drugtime document id
so I did the following :

 ConfirmDrugTaken(DateTime d) async {
    final User? user = FirebaseAuth.instance.currentUser;
    final _uid = user?.uid;
    var drugID="";
    // Get the user's sub-collections in Firestore
    final QuerySnapshot<Map<String, dynamic>> querySnapshot =
    await FirebaseFirestore.instance
        .collection("users")
        .doc(_uid)
        .collection('drug').where("drugName", isEqualTo: widget.title)
        .get();
    querySnapshot.docs.forEach((element) async {
      drugID=element.id;
    });

    final QuerySnapshot<Map<String, dynamic>> querySnapshot2 =FirebaseFirestore.instance
        .collection("users")
        .doc(_uid)
        .collection("drug")
        .doc(drugID).collection("drugDates").where('time',isEqualTo: d).get() as QuerySnapshot<Map<String, dynamic>>;
    querySnapshot2.docs.forEach((element) async {
      FirebaseFirestore.instance
          .collection("users")
          .doc(_uid)
          .collection("drug")
          .doc(drugID).collection("drugDates").doc(element.id).update( {'isTaken': true});

    });


  } 

but this error occur:

[ERROR:flutter/runtime/dart_vm_initializer.cc(41)] Unhandled Exception: type 'Future<QuerySnapshot<Map<String, dynamic>>>' is not a subtype of type 'QuerySnapshot<Map<String, dynamic>>' in type cast
E/flutter (17976): #0      _drugSetupState.ConfirmDrugTaken (package:taafi_application_v1/pages/drug_setup.dart:215:79)
E/flutter (17976): <asynchronous suspension>
E/flutter (17976): #1      _drugSetupState.setAlarm.<anonymous closure>.<anonymous closure>.<anonymous closure>.<anonymous closure> (package:taafi_application_v1/pages/drug_setup.dart:112:20)
E/flutter (17976): <asynchronous suspension>

Is there is another way to enter to the sub-sub-collection with out knowing the id OR how can I fix this error?

please help

>Solution :

You forgot to use await to call async method, code should be as follows for querySnapshot2

final QuerySnapshot<Map<String, dynamic>> querySnapshot2 = (await FirebaseFirestore.instance
        .collection("users")
        .doc(_uid)
        .collection("drug")
        .doc(drugID).collection("drugDates").where('time',isEqualTo: d).get()) as QuerySnapshot<Map<String, dynamic>>;