Updating an array within mongdbo document [Golang]

I'm trying to update an array item within a mongo document.

Event is the Document, which i'm finding with the event id, then i need to identify which object in the task array needs to be changed by identifying the name of the task.

Any idea where i'm going wrong

Event Stuct

type Event struct {
EventId              string       `json:"eventid" bson:"eventid"`
EventOwner           string       `json:"eventowner" bson:"eventowner"`
EventTitle           string       `json:"eventtitle" bson:"eventtitle"`
EventDateTime        string       `json:"eventdatetime" bson:"eventdatetime"`
EventLocation        EventAddress `json:"eventlocation" bson:"eventlocation"`
EventTotalTicket     int          `json:"eventtotalticket" bson:"eventtotalticket"`
EventAvailableTicket int          `json:"eventavailableticket" bson:"eventavailableticket"`
EventCoverImage      string       `json:"eventcoverimage" bson:"eventcoverimage"`
EventDescription     string       `json:"eventdescription" bson:"eventdescription"`
Lat                  string       `json:"lat" bson:"lat"`
Long                 string       `json:"long" bson:"long"`
Task                 []Task       `json:"task" bson:"task"`
}

Task Struct:

type Task struct {
TaskTitle    string  `json:"tasktitle" bson:"tasktitle"`
InitalBudget float32 `json:"initialbudget" bson:"initialbudget"`
Supplier     string  `json:"suppid" bson:"suppid"`
AgreedPrice  float32 `json:"agreedprice" bson:"agreedprice"`
IsComplete   bool    `json:"iscomplete" bson:"iscomplete"`
}

Here's what i'm trying to do

func (e *EventServiceImpl) UpdateTask(eventid *string, task *models.Task) error {

    //filter := bson.D{bson.E{Key: "eventid", Value: eventid}, bson.E{Key: "tasktitle", Value: task.TaskTitle}}
    filter := bson.M{"$and": []bson.M{{"eventid": eventid}, {"task": bson.E{Key: "tasktitle", Value: task.TaskTitle}}}}
    update := bson.D{bson.E{Key: "$set", Value: bson.D{bson.E{Key: "task", Value: bson.M{"tasktitle": task.TaskTitle, "initialbudget": task.InitalBudget, "suppid": task.Supplier, "agreedprice": task.AgreedPrice, "iscomplete": task.IsComplete}}}}}
    result, _ := e.eventcollection.UpdateOne(e.ctx, filter, update)
    if result.MatchedCount != 1 {
        return errors.New("No matched document found to update")
    }
    return nil

}

I always receive the "No matched document found to update"

Here was the solution

func (e *EventServiceImpl) UpdateTask(eventid *string, task *models.Task) error {
	filter := bson.M{"eventid": eventid, "task": bson.M{"$elemMatch": bson.M{"tasktitle": task.TaskTitle}}}
	update := bson.M{"$set": bson.M{"task.$.initialbudget": task.InitalBudget, "task.$.suppid": task.Supplier, "task.$.agreedprice": task.AgreedPrice, "task.$.iscomplete": task.IsComplete}}
	result, err := e.eventcollection.UpdateOne(e.ctx, filter, update)
	if err != nil {
		return err
	}
	if result.MatchedCount != 1 {
		return errors.New("No matched document found to update")
	}
	return nil
}