'No write concern mode named 'majority`' found in replica set configuration' error

I'm trying to insert an object into mongodb via a POST request. The object that I send gets inserted in the db successfully, however I get the error mentioned above.

The package I'm using for mongo db:

https://github.com/mongodb/mongo-go-driver

Connection string

mongodb+srv://user:password@bookcluster.pxcqs.mongodb.net/DBname?retryWrites=true&w=majority`

The way I set up the database connection:

var DbConn *mongo.Client //*sql.DB //*mongo.Clientfunc SetupDB(conn_str string) {    var err error    DbConn, err = mongo.NewClient(options.Client().ApplyURI(conn_str))    if err != nil {        log.Fatal(err)    }    ctx, _ := context.WithTimeout(context.Background(), 10*time.Second)    err = DbConn.Connect(ctx)    if err != nil {        log.Fatal(err)    }}

My object:

package bookimport "go.mongodb.org/mongo-driver/bson/primitive"type Book struct {    Id        primitive.ObjectID `json:"id,omitempty" bson:"_id,omitempty"`    Title     string             `json:"title" bson:"title"`    Author    string             `json:"author" bson:"author"`    Year      int                `json:"year" bson:"year"`    ShortDesc string             `json:"shortDesc" bson:"shortDesc"`    Genre     string             `json:"genre" bson:"genre"`}

Here's how I send the request inside insertBook() (where b is of type Book):

ctx, cancel := context.WithTimeout(context.Background(), 3*time.Second)    defer cancel()    result, err := database.DbConn.Database(dbName).Collection(collectionName).InsertOne(ctx, b)

Full error text:

multiple write errors: [{write errors: []},{(UnknownReplWriteConcern) No write concern mode named 'majority`'found in replica set configuration}]

My request in Postman

I'm not sure if I'm missing some sort of a configuration setting somewhere - I just started with mongoDBI tried to follow the example set in these tutorials: 3, 4 and they don't seem to mention anything about the 'write concern' and 'majority'.Also tried looking into the documentation and googling the error but didn't find anything helpful.