How to call the API in Android(Retrofit)
//Main Class

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.util.Log
import android.widget.Toast
import com.example.demoapicall.network.ApiInterface
import com.example.demoapicall.network.ServiceClient
import io.reactivex.android.schedulers.AndroidSchedulers
import io.reactivex.disposables.CompositeDisposable
import io.reactivex.schedulers.Schedulers
import kotlinx.android.synthetic.main.activity_main.*
import org.json.JSONObject
import retrofit2.HttpException

class MainActivity : AppCompatActivity() {
  
     private var mCompositeDisposable: CompositeDisposable? = null 

     private var apiService: ApiInterface? = null 

     override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        //Init 

         init()
        //Gett Data
        btnGetData.setOnClickListener { 

      getData()
        }
    }

    private fun getData() {
        mCompositeDisposable?.add(
            apiService!!.updateProfile(
                "7   ",
                "435",
                "6",
                "7",
                "6",
                "7"            )
                .observeOn(AndroidSchedulers.mainThread())
                .subscribeOn(Schedulers.io())
                .subscribe(this::handleResponse, this::handleError)
        )
    }

    private fun init() {
        apiService =
            ServiceClient().getClientHeader("your token")
                .create(ApiInterface::class.java)
        mCompositeDisposable = CompositeDisposable()
    }

    //Getting the Response Here 

       private fun handleResponse(loginResponse: LoginResponse) {
        if (loginResponse.status == 200) {
            Toast.makeText(this, loginResponse.message, Toast.LENGTH_SHORT).show()

        } else {
            Toast.makeText(this, loginResponse.message, Toast.LENGTH_SHORT).show()
        }
    }

    private fun handleError(error: Throwable) {
        Log.i("", "handleError: $error")
        Log.i("", "handleError: $error")
        if (error is HttpException) {
            val errorBody = error.response().errorBody()!!.string();
            val jsonObject = JSONObject(errorBody)
            if (jsonObject.optInt("status") == 203) {
            } else if (jsonObject.optInt("status") == 205) {
            } else if (jsonObject.optInt("status") == 201) {
            } else {
                Toast.makeText(this, "Authentication Failed", Toast.LENGTH_SHORT).show()
            }
        }
    }
}

//Api Interface
import com.example.demoapicall.LoginResponse
import io.reactivex.Observable
import okhttp3.RequestBody
import retrofit2.Call
import retrofit2.http.*
import retrofit2.http.Multipartimport retrofit2.http.POST

interface ApiInterface {
    @FormUrlEncoded    @POST("api / your end url")
    fun updateProfile(
        @Field("parameter 1") user_id: String,
        @Field("parameter 2") about: String,
        @Field("parameter 3") course: String,
        @Field("parameter 4") year_of_study: String,
        @Field("parameter 5") gender: String,
    
    ): Observable<Your Model>

}

//Service client
import okhttp3.ConnectionSpec
import okhttp3.OkHttpClient
import okhttp3.logging.HttpLoggingInterceptor
import retrofit2.Retrofit
import retrofit2.adapter.rxjava2.RxJava2CallAdapterFactory
import retrofit2.converter.gson.GsonConverterFactory
import java.util.*
import java.util.concurrent.TimeUnit

public class ServiceClient {
    private lateinit var interceptor: HttpLoggingInterceptor
    private lateinit var okHttpClient: OkHttpClient
    private var retrofit: Retrofit? = null

//For with out token    val client: Retrofit
        get() {
            interceptor = HttpLoggingInterceptor()
            interceptor.level = HttpLoggingInterceptor.Level.BODY 

            okHttpClient = OkHttpClient.Builder()
                .addInterceptor(interceptor)
                .connectionSpecs(Arrays.asList(ConnectionSpec.MODERN_TLS, ConnectionSpec.COMPATIBLE_TLS))
                .followRedirects(true)
                .followSslRedirects(true)
                .retryOnConnectionFailure(true)
                .connectTimeout(20, TimeUnit.SECONDS)
                .readTimeout(20, TimeUnit.SECONDS)
                .writeTimeout(20, TimeUnit.SECONDS)
                .cache(null)
                .build()
            if (retrofit == null) {
                retrofit = Retrofit.Builder()
                    .baseUrl("your base url")
                    .addConverterFactory(GsonConverterFactory.create())
                    .client(okHttpClient)
                    .build()
            }
            return retrofit!!

        }
//For require token
    fun getClientHeader(header: String): Retrofit {
        val httpLoggingInterceptor = HttpLoggingInterceptor()
        httpLoggingInterceptor.setLevel(HttpLoggingInterceptor.Level.BODY)
        val httpClient = OkHttpClient.Builder()
        httpClient.addInterceptor { chain -> 

         val original = chain.request()
            val request = original.newBuilder()
                .header("Authorization", header)
                .method(original.method(), original.body())
                .build()
            chain.proceed(request)
        }
        httpClient.interceptors().add(httpLoggingInterceptor)
        httpClient.readTimeout(120, TimeUnit.SECONDS)
        httpClient.connectTimeout(120, TimeUnit.SECONDS)

        val client = httpClient.build()
        retrofit = Retrofit.Builder()
            .baseUrl("your base url")
            .addConverterFactory(GsonConverterFactory.create())
            .addCallAdapterFactory(RxJava2CallAdapterFactory.create())
            .client(client)
            .build()

        return retrofit!!
    }

} 

//Need to add libary in Gradle 

implementation 'com.squareup.retrofit2:adapter-rxjava:2.4.0'

implementation 'com.squareup.retrofit2:converter-gson:2.4.0'

implementation 'com.squareup.retrofit2:retrofit:2.4.0' 

implementation 'com.squareup.retrofit2:adapter-rxjava:2.4.0'

implementation 'com.squareup.retrofit2:converter-gson:2.4.0'

implementation 'com.jakewharton.retrofit:retrofit2-rxjava2-adapter:1.0.0'

implementation 'io.reactivex.rxjava2:rxandroid:2.1.0'

implementation 'com.squareup.okhttp3:logging-interceptor:3.4.1'

implementation 'com.squareup.okhttp3:okhttp:3.4.1'

implementation "com.squareup.retrofit2:retrofit:2.0.0"

implementation "com.squareup.retrofit2:converter-gson:2.0.0"

implementation 'com.squareup.retrofit2:retrofit:2.3.0'

implementation 'com.squareup.retrofit2:converter-gson:2.3.0'

implementation 'com.squareup.retrofit2:adapter-rxjava2:2.3.0'

implementation 'io.reactivex.rxjava2:rxjava:2.1.6'

implementation 'io.reactivex.rxjava2:rxandroid:2.0.1'