Getting Error in GraphQL Mutation using AWS Amplify in react native app

Trying to execute a graphql mutation, where the mutation should take custom type. In the App Sync schema, I have defined these custom Types:

Schema:

  input CreateConversationInput {
        user: UserInput
        doctor: DoctorInput
        questionsAndAnsers: [ConversationQAInput]
        pet: UpdatePetInput
    }

React Native Code:

  const createConversationInput = {

        user: {
            username: "deep",
            userType: "Patient",
            fullName: "Deep A"
        },
        doctor: {
            name: "Raman",
            speciality: "dog",
            doctorId: "0bd9855e-a3f2-4616-8132-aed490973bf7"
        },
        questionsAndAnswers: [{ question: "Question 1", answer: "Answer 1" }, { question: "Question 2", answer: "Answer 2" }],
        pet: { username: "deep39303903", petId: "238280340932", category: "Canine" }


    }

    API.graphql(graphqlOperation(CreateConversation, createConversationInput)).then(response => {

        console.log(response);

    }).catch(err => {
        console.log(err);
    });

I have define mutation like this:

export const CreateConversation = `mutation CreateConversation( $user: Object, 
    $doctor: Object, $questionsAndAnswers: Object, $pet: Object ) {

        createConversation(

             input : {

                user: $user
                doctor: $doctor
                questionsAndAnswers: $questionsAndAnswers
                pet: $pet
            }
        ){
    username
    createdAt

  }

  }`;

The mutation is working properly from the AWS GraphQL console. However, in the react native app, I get error.

Error:

"Validation error of type UnknownType: Unknown type Object".

I believe the error is because I defined the type as Object in mutations instead of the actual type defined in the AWS Schema. How can I define custom types in the React Native code if this is the issue?

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