It's too late to answer, sorry about it, for creating the below body:
{
    "username": "ًRajab",
    "email": "rajab.mohammadi@gmail.com",
    "phone": "+93767626554",
    "password": "123asd",
    "carType": "600fdcc646bc6409ae97e2ab",
    "fcmToken":"lljlkdsajfljasldfj;lsa",
    "profilePhoto": "https://st.depositphotos.com/2101611/3925/v/600/depositphotos_39258143-stock-illustration-businessman-avatar-profile-picture.jpg",
    "documents": {
        "DL": [
            {
                "_id": "5fccb687c5b4260011810125",
                "uriPath": "https://webfume-onionai.s3.amazonaws.com/guest/public/document/326634-beats_by_dre-wallpaper-1366x768.jpg"
            }
        ],
        "Registration": [
            {
                "_id": "5fccb687c5b4260011810125",
                "uriPath": "https://webfume-onionai.s3.amazonaws.com/guest/public/document/326634-beats_by_dre-wallpaper-1366x768.jpg"
            }
        ],
        "Insurance":[
              {
                "_id": "5fccb687c5b4260011810125",
                "uriPath": "https://webfume-onionai.s3.amazonaws.com/guest/public/document/326634-beats_by_dre-wallpaper-1366x768.jpg"
            }
        ],
         "CarInside":[
              {
                "_id": "5fccb687c5b4260011810125",
                "uriPath": "https://webfume-onionai.s3.amazonaws.com/guest/public/document/326634-beats_by_dre-wallpaper-1366x768.jpg"
            }
        ],
         "CarOutside":[
              {
                "_id": "5fccb687c5b4260011810125",
                "uriPath": "https://webfume-onionai.s3.amazonaws.com/guest/public/document/326634-beats_by_dre-wallpaper-1366x768.jpg"
            }
        ]
    }
}
You can create dynamically like the below code:
JSONObject jsonBody = new JSONObject();
try {
    jsonBody.put("username", userName);
    jsonBody.put("email", email);
    jsonBody.put("phone", contactNumber);
    jsonBody.put("password", password);
    jsonBody.put("carType", carType);
    jsonBody.put("fcmToken", "lljlkdsajfljasldfj;lsa");
    jsonBody.put("profilePhoto", "https://st.depositphotos.com/2101611/3925/v/600/depositphotos_39258143-stock-illustration-businessman-avatar-profile-picture.jpg");
    JSONObject document = new JSONObject();
    try {
        document.put("DL", createDocument("5fccb687c5b4260011810125", "https://st.depositphotos.com/2101611/3925/v/600/depositphotos_39258143-stock-illustration-businessman-avatar-profile-picture.jpg"));
        document.put("Registration", createDocument("5fccb687c5b4260011810125", "https://st.depositphotos.com/2101611/3925/v/600/depositphotos_39258143-stock-illustration-businessman-avatar-profile-picture.jpg"));
        document.put("Insurance", createDocument("5fccb687c5b4260011810125", "https://st.depositphotos.com/2101611/3925/v/600/depositphotos_39258143-stock-illustration-businessman-avatar-profile-picture.jpg"));
        document.put("CarInside", createDocument("5fccb687c5b4260011810125", "https://st.depositphotos.com/2101611/3925/v/600/depositphotos_39258143-stock-illustration-businessman-avatar-profile-picture.jpg"));
        document.put("CarOutside", createDocument("5fccb687c5b4260011810125", "https://st.depositphotos.com/2101611/3925/v/600/depositphotos_39258143-stock-illustration-businessman-avatar-profile-picture.jpg"));
    } catch (JSONException e) {
        e.printStackTrace();
    }
    jsonBody.put("documents", document.toString());
    Log.i("MAHDI", "Hello: Mahdi: Data: " + jsonBody);
} catch (JSONException e) {
    e.printStackTrace();
}
And the createDocument method code:
public JSONArray createDocument(String id, String imageUrl) {
    JSONObject dlObject = new JSONObject();
    try {
        dlObject.put("_id", id);
        dlObject.put("uriPath", imageUrl);
    } catch (JSONException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    JSONArray dlArray = new JSONArray();
    dlArray.put(dlObject);
    return dlArray;
    }