field must be of BSON type object

Your filter variable is an array, not an object and a find() query accepts an object, not an array. Your final filter object should have this structure, for example

var filter = {    "$and": [        { sel: parseInt(query.idx) },        { admn: parseInt(query.idx)}    ],    "$or": [        { uid: {$exists: false} },        { uid: 0 },        { uid: null}    ]}

So you need to change the part

var filter = [];filter.push({$and: andQry});// = [$and : {andQry}, {$or: orQry}];logger.debug("filter : ",filter);

to

var filter = {};filter["$and"] = andQry;filter["$or"] = orQry;logger.debug("filter : ",filter);

Find expected values in the particular date range to get an output by using Find() Keyword , to get all the array of listed outputs use All()

    db := GetDB()    defer db.Session.Close()    var tempMeet []models.Meetings    gtQuery := bson.M{"$gt": start}    ltQuery := bson.M{"$lt": end}    pipe := bson.M{        "$and": []bson.M{            bson.M{"startTime": gtQuery},            bson.M{"endTime": ltQuery},        },    }    shared.BsonToJSONPrint(pipe)    err := db.C(models.COLLECTIONNAME).Find(pipe).All(&tempMeet)    if err != nil {        fmt.Println(err)        return nil, errors.New(err.Error())    }    return tempMeet, nil