Unable to update the document

HI All, I’m using MongoDB in Ktor backend server.

I have a below data class

@Serializable
data class Teachers(
    @SerialName("_id")
    @Serializable(with = ObjectIdAsStringSerializer::class)
    val id: ObjectId = ObjectId(),
    val teacherId: String,
    val salutation: String,
    val firstName: String,
    val lastName: String,
    val address: Address,
    val email: String,
    val dob: String,
    val gender: String,
    val nationality: String,
    val phone: String,
    val subject: HashMap<String, String>,
    val profileImage: String,
    val timetable: List<TimetableEntry> = emptyList() // List to track the teacher's timetable
) 

@Serializable
data class TimetableEntry(
    val day: String,       // e.g., "Monday"
    val startTime: String, // "08:30"
    val endTime: String,   // "10:00"
)

schoolTeacherDb.updateOne(
            Filters.eq("teacherId", teacherId),
            Updates.addToSet("timetable", TimetableEntry(
                day = day,
                startTime = startTime,
                endTime = endTime,
            ))
        ).wasAcknowledged()

This is run thorugh an api which return 200 status , there are no error in mongodb logs but the document is not getting updated

I also tried Push and set methods, but still the outcome. There is no error api also returns 200 . but document does not get update in the DB.

Adding the code for the route which makes the api call

post("v1/teacher/update/timetable") {
            val teacherId = call.parameters["teacherId"]
            val update = call.receive<TimetableEntryUpdate>()

            if (teacherId == null) {
                call.respond(HttpStatusCode.BadRequest, "Teacher ID is required")
                return@post
            }
            try {
                val teacherUpdated = schoolTeacherDb?.updateTeacherTimeTable(
                    teacherId = teacherId,
                    day = update.day,
                    startTime = update.startTime,
                    endTime = update.endTime
                )

                if (teacherUpdated == true) {
                    call.respond(HttpStatusCode.OK, SimpleResponse(true, "Timetable Updated for the teacher"))
                } else {
                    call.respond(HttpStatusCode.OK, SimpleResponse(false,"Timetable Not Updated"))
                }
            } catch (e: Exception) {
                call.respond(HttpStatusCode.Conflict,e.printStackTrace()?:"Error, please contact support")
            }
        }