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

Android 4.4 (works for me)

def ok_http_version = "3.11.0"
implementation "com.squareup.okhttp3:okhttp:$ok_http_version"
implementation "com.squareup.okhttp3:logging-interceptor:$ok_http_version"