For minSDK lower than 21, change your OkHttp version to 3.12.12 in gradle like this –
//OkHttp
implementation ("com.squareup.okhttp3:okhttp:3.12.12"){
force = true //API 19 support
}
implementation 'com.squareup.okhttp3:logging-interceptor:3.12.12'
It should work fine!