How to fix Expected Android API level 21+ but was 19 in Android

Question

In my application i want get data from server, for get connect to server i used Retrofit, OkHttp.
But when running application, show me

Answer 1

Thanks @ https://stackoverflow.com/users/5773044/anupam This code works in Android API 19:

// Note: 3.12.+ to support Android API 19
implementation 'com.squareup.okhttp3:okhttp:3.12.10'
implementation 'com.squareup.okhttp3:logging-interceptor:3.12.10'

implementation 'io.reactivex.rxjava2:rxkotlin:2.4.0'
implementation 'io.reactivex.rxjava2:rxandroid:2.1.1'

implementation 'com.squareup.retrofit2:adapter-rxjava2:2.6.4'
implementation 'com.squareup.retrofit2:converter-gson:2.6.4'
implementation 'com.squareup.retrofit2:converter-scalars:2.6.4'
testImplementation 'com.squareup.retrofit2:retrofit-mock:2.6.4'
androidTestImplementation 'com.squareup.retrofit2:retrofit-mock:2.6.4'