show progress bar before fetching data from server using retrofit

I couldn't help but notice that your repository contains lots of repetitive code. first point to learn here is that all that logic in Repository, it usually goes in the ViewModel. second thing is that you are using applicationScope to launch your coroutines, which usually is done using viewModelScope(takes care of cancellation) object which is available in every viewModel.

So first we have to take care of that repetitive code and move it to ViewModel. So your viewModel would now look like

class YourViewModel: ViewModel() {
    // Your other init code, repo creation etc

    // Live data objects for progressBar and error, we will observe these in Fragment/Activity
    val showProgress: MutableLiveData<Boolean> = MutableLiveData()
    val errorMessage: MutableLiveData<String> = MutableLiveData()

    /**
      * A Generic api caller, which updates the given live data object with the api result 
      * and internally takes care of progress bar visibility. */
    private fun <T> callApiAndPost(liveData: MutableLiveData<T>,
                                   apiCall: () -> Response<T> ) = viewModelScope.launch {
        try{
            showProgress.postValue(true)   // Show prgress bar when api call is active
            if(result.code() == 200) { liveData.postValue(result.body())  }
            else{ errorMessage.postValue("Network call failed, try again") }
            showProgress.postValue(false)
        }
        catch (e: Exception){
            errorMessage.postValue("Network call failed, try again")
            showProgress.postValue(false)
        }
    }
    
    /******** Now all your API call methods should be called as *************/

    // First declare the live data object which will contain the api result
    val sliderData: MutableLiveData<List<Model.Slider>> = MutableLiveData()

    // Now call the API as
    fun getSliderImages() = callApiAndPost(sliderData) {
        repository.getSliderImages()
    }
}

After that remove all the logic from Repository and make it simply call the network methods as

suspend fun getSliderImages() = api.getSliderImages()   // simply delegate to network layer

And finally to display the progress bar, simply observe the showProgress LiveData object in your Activity/Fragment as

viewModel.showProgress.observer(this, Observer{
    progressBar.visibility = if(it) View.VISIBLE else View.GONE
}

First create a enum class status:

enum class Status {
SUCCESS,
ERROR,
LOADING
}

Then create resource class like this:

data class Resource<out T>(val status: Status, val data: T?, val message: String?) {

companion object {

    fun <T> success(data: T?): Resource<T> {
        return Resource(Status.SUCCESS, data, null)
    }

    fun <T> error(msg: String, data: T?): Resource<T> {
        return Resource(Status.ERROR, data, msg)
    }

    fun <T> loading(data: T?): Resource<T> {
        return Resource(Status.LOADING, data, null)
    }

  }

} 

Now add your request to a list of response:

var list = java.util.ArrayList<Response<*>>()
suspend fun getApis() = list.addAll(
    listOf(
        api.advertise(),
        api.getAmazingProduct(),
        api.dailyShoes(),
        api.getSliderImages(),
         .
         .
         .
    )
)

In your viewmodel class:

private val _apis = MutableLiveData<Resource<*>>()
val apis: LiveData<Resource<*>>
    get() = _apis

init {
    getAllApi()
}

fun getAllApi() {
    val job = Job()
    viewModelScope.launch(IO + job) {
        _apis.postValue(
            Resource.loading(null)
        )
        delay(2000)
        repository.getApis().let {
            withContext(Main + SupervisorJob(job)) {
                it.let {
                    if (it) {
                        _apis.postValue(Resource.success(it))
                    } else {
                        _apis.postValue(Resource.error("Unknown error eccured", null))
                    }
                }
            }
        }
        job.complete()
        job.cancel()
    }
}

Now you can use status to show progress like this . use this part in your target fragment:

 private fun setProgress() {
    viewModel.apis.observe(viewLifecycleOwner) {
        when (it.status) {
            Status.SUCCESS -> {
                binding.apply {
                    progress.visibility = View.INVISIBLE
                    line1.visibility = View.VISIBLE
                    parentscroll.visibility = View.VISIBLE
                }
            }
            Status.ERROR -> {
                binding.apply {
                    progress.visibility = View.INVISIBLE
                    line1.visibility = View.INVISIBLE
                    parentscroll.visibility = View.INVISIBLE
                }
            }
            Status.LOADING -> {
                binding.apply {
                    progress.visibility = View.VISIBLE
                    line1.visibility = View.INVISIBLE
                    parentscroll.visibility = View.INVISIBLE
                }
            }
        }
    }
}

I hope you find it useful.